Method and apparatus for providing connection with radio access network through wireless backhaul

ABSTRACT

The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as long term evolution (LTE). According to the present disclosure, a method for providing a connection with a radio access network via a wireless backhaul comprises determining one of a first state in which a first node connected with the radio access network is operated using all of beams and a second state in which the first node is operated using an beam of the first node determined in the first state as an operation mode of the first node and providing, by the first node, the connection with the radio access network to a radio access node in the determined operation mode.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to and claims the benefit under 35U.S.C. § 119(a) of a Korean patent application filed in the KoreanIntellectual Property Office on Aug. 13, 2015 and assigned Serial No.10-2015-0114605, the entire disclosure of which is incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure concerns technology for providing a connectionwith a radio access network through a backhaul network, and morespecifically, to methods and apparatuses for wireless backhaulcommunication by backhaul nodes providing network connection to radioaccess nodes based on beamforming.

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of 4G (4th-Generation) communication systems, efforts havebeen made to develop an improved 5G (5th-Generation) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘beyond 4G network’ or a ‘post LTE system’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, hybrid FSK and QAM modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

Meanwhile, wireless backhaul schemes may break down into point-to-point(PTP) wireless backhaul and point-to-multipoint (PMP) wireless backhaul.PTP wireless backhaul offers one-to-one communication between onetransmitter and one receiver. In PTP wireless backhaul, accordingly, therespective antennas of the transmitter and the receiver are commonlyinstalled in fixed directions that give the optimal performance withrespect to each other while generating very narrow beams. Here, use ofthe higher frequency may further narrow beams generated by antennas withthe same size while increasing antenna gain. Therefore, PTP wirelessbackhaul is more advantageous for high frequency and benefits in lightof less interference and excellent communication performance through anincreased antenna gain. However, the need of being installed with beamoriented accurately at the position where line-of-sight (LOS) isattained results in wireless backhaul being primarily intended for broadservice coverage macro base stations, but not adequate for base stationswith relatively smaller coverage (referred to, hereinafter, as smallcell base stations).

In PMP wireless backhaul, meanwhile, one hub node (HN) connected with awired backhaul offers a network connection by wirelessly communicatingwith multiple remote backhaul nodes (RBN). Conventionally, PMP backhauladopts antennas with a large beam width of about 60 degrees to about 90degrees at 6 GHz or less. For the reasons, PMP backhaul, despite beingcapable of communication even under a non-line-of-sight (NLOS)environment, is vulnerable to interference and exhibits poorcommunication performance due to the backhaul's decreased antenna gain.Thus, PMP wireless backhaul gives more advantages to small cell basestations that have reduced communication capacity but require easyinstallation of multiple RBNs regardless of position.

Recently, vigorous research and 3GPP long term evolution (LTE)standardization are underway for heterogeneous cell technology foradding small cells in macro cell service coverage for maximized serviceareal capacity. As a result, future mobile communication systems areexpected to present significantly increased small cell capacity due tocoexistence of a number of small cells in macro cells. However,conventional PMP wireless backhaul cannot afford to meet capacityrequirements for future small cells due to tiny communication capacity.Conventional PTP wireless backhaul costs a lot for installation andoperation, albeit with more communication capacity than that of PMPbackhaul. Therefore, a need exists for schemes for increasing small cellbackhaul capacity in future mobile communication systems.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

The present disclosure discloses a scheme for operating a PMP wirelessbackhaul that is easy to install and operate and has a largecommunication capacity in hierarchical cell mobile communication system.

The present disclosure may lead to minimized interference and maximizedcommunication efficiency by generating transmission/reception beams witha very high antenna gain at a high frequency and communicating signals.

To address the above-discussed deficiencies, it is a primary object toprovide, a method for providing a connection with a radio access networkvia a wireless backhaul comprises determining one of a first state inwhich a first node connected with the radio access network is operatedusing all of beams and a second state in which the first node isoperated using an beam of the first node determined in the first stateas an operation mode of the first node and providing, by the first node,the connection with the radio access network to a radio access node inthe determined operation mode.

According to an embodiment of the present disclosure, a method forproviding a connection with a radio access network via a wirelessbackhaul comprises when a second node connected with the radio accessnetwork meets a first state transition condition, operating in a firststate where all of beams are used to determine an first node connectedwith the radio access network and an beam based on a signal receivedthrough all of the beams and accessing the first node to communicatewith the first node.

According to an embodiment of the present disclosure, an apparatus forproviding a connection with a radio access network via a wirelessbackhaul comprises a transceiver communicating with a first nodeconnected with the radio access network and a controller determining oneof a first state in which the first node is operated using all of beamsand a second state in which the first node is operated using an beam ofthe first node determined in the first state as an operation mode of thefirst node and controlling the transceiver so that the first nodeprovides the connection with the radio access network to a radio accessnode in the determined operation mode.

According to an embodiment of the present disclosure, 32. A second nodefor providing a connection with a radio access network via a wirelessbackhaul comprises when the second node connected with the radio accessnetwork meets a first state transition condition, a controller operatesin a first state where all of beams are used to determine an first nodeconnected with the radio access network and an beam based on a signalreceived through all of the beams and a transceiver accessing the firstnode to communicate with the first node.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the disclosure.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an example of a wireless backhaul configurationproviding a network connection to a small cell base station (SBS) in amobile communication system according to an embodiment of the presentdisclosure;

FIG. 2 illustrates an operation state transition of an HN according toan embodiment of the present disclosure;

FIG. 3 illustrates a state transition of a RBN according to anembodiment of the present disclosure;

FIG. 4 illustrates an example of a frame structure according to anembodiment of the present disclosure, wherein according to an embodimentof the present disclosure, the exemplified frame structure is one usedfor cellular mobile communication, for ease of description;

FIG. 5 illustrates an example of configuring an SS and BCH in a frameaccording to an embodiment of the present disclosure;

FIGS. 6a and 6b illustrate examples of configuring a DL control slot andUL control slot in a frame according to an embodiment of the presentdisclosure;

FIG. 7 illustrates an example of configuring a DL and UL data slot in aframe according to an embodiment of the present disclosure;

FIG. 8 illustrates an example of configuring a BM slot in a frameaccording to an embodiment of the present disclosure;

FIG. 9 illustrates an example of configuring a UL RACH slot in a frameaccording to an embodiment of the present disclosure;

FIG. 10 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated in a BUS according to an embodiment ofthe present disclosure;

FIG. 11 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated in a BOCS, and the communication mode isan FBM according to an embodiment of the present disclosure;

FIG. 12 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated in a BOCS, and the communication mode isan ABM according to an embodiment of the present disclosure;

FIG. 13 illustrates an example of an applicable beacon interval (BI)structure according to an embodiment of the present disclosure;

FIG. 14 illustrates beams used for transmission and reception ofinformation and slots when HNs and RBNs configuring a wireless backhaulare operated in a BUS according to an embodiment of the presentdisclosure;

FIG. 15 illustrates beams used when HNs and RBNs configuring a wirelessbackhaul are operated in an FBM of a BOCS according to an embodiment ofthe present disclosure;

FIG. 16 illustrates a beam used when HNs and RBNs configuring a wirelessbackhaul are operated in an ABM of a BOCS according to an embodiment ofthe present disclosure;

FIG. 17 illustrates a result obtained through a wireless backhauloperated in a BUS according to an embodiment of the present disclosure;

FIG. 18 illustrates an installation structure for a RAN and backhaulnode (BN) according to an embodiment of the present disclosure;

FIG. 19 illustrates a structure of an antenna for radio access and anantenna for wireless backhaul according to an embodiment of the presentdisclosure;

FIG. 20 illustrates an example of a radio access network where awireless backhaul is installed according to an embodiment of the presentdisclosure;

FIG. 21 illustrates an example of a S1 user plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure;

FIG. 22 illustrates an example of an X2 user plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure;

FIG. 23 illustrates an example of an S1 control plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure;

FIG. 24 illustrates an example of an X2 control plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure;

FIG. 25 illustrates an example of a wireless control plane protocolstack structure for supporting an operation of an HN and RBN configuringa wireless backhaul according to an embodiment of the presentdisclosure;

FIG. 26 illustrates an example of a wireless user plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure;

FIGS. 27a and 27b illustrate examples of an operation flow of a firstcase of BUS transition conditions according to an embodiment of thepresent disclosure;

FIGS. 28a, 28b, and 28c illustrate examples of an operation flow of asecond case of the BUS transition conditions according to an embodimentof the present disclosure;

FIGS. 29a, 29b, 29c, and 29d illustrate examples of an operation flow ofa third case of the BUS transition conditions according to an embodimentof the present disclosure;

FIG. 30 illustrates an example of an operation flow of a fourth case ofthe BUS transition conditions according to an embodiment of the presentdisclosure;

FIG. 31 illustrates an operation flow of an RBN according to anembodiment of the present disclosure;

FIG. 32 illustrates an operation flow of an RBN according to anotherembodiment of the present disclosure;

FIGS. 33a, 33b, and 33c illustrate an example of an operation mode of anHN operated in a BOCS and a communication mode transition operationaccording to an embodiment of the present disclosure; and

FIG. 34 illustrates an example of a configuration of a backhaul node andRAN according to an embodiment of the present disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

FIGS. 1 through 34, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged electronic device.

Hereinafter, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. The same referencenumerals are used to refer to same elements throughout the drawings.When determined to make the subject matter of the present disclosureunclear, the detailed of the known functions or configurations may beskipped. The terms as used herein are defined considering the functionsin the present disclosure and may be replaced with other terms accordingto the intention or practice of the user or operator. Therefore, theterms should be defined based on the overall disclosure.

According to an embodiment of the present disclosure, a wirelessbackhaul includes at least one hub node (HN) and at least one remotebackhaul node (RBN). Each HN is connected to a network through a wiredbackhaul or another wireless backhaul and performs wireless backhaulcommunication with one or more RBNs. According to an embodiment of thepresent disclosure, the HN uses a point-to-multipoint (PMP) wirelessbackhaul technology for providing a network connection to a radio accessnode (RAN) connected with at least one RBN through wireless backhaulcommunication. Here, the RAN corresponds to a base station (BS) in amobile communication system and provides a network connection to amobile station (MS) through mobile communication. According to anembodiment of the present disclosure, such an example is assumed anddescribed that signal communication is conducted using a beamformingantenna generating very narrow beams at a high frequency, e.g., 6 GHz ormore.

FIG. 1 illustrates an example of a wireless backhaul configurationproviding a network connection to a small cell base station (SBS) in amobile communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1, as an example, an HN 110 a is installed togetherwith a macro cell BS (MBS) 110, a RBN1 120 a is installed along with asmall cell base station 1 (SBS1) 120, and a RBN2 130 a is installedalong with an SBS2 130. The HN 110 a may afford a network connection tothe SBS1 120 and SBS2 130 by simultaneously providing wireless backhaulcommunication to the RBN1 120 a and RBN2 130 a.

The MBS 110 provides radio access for mobile communication to a MS11111, and the SBS1 120 and SBS2 130, respectively, provide radio accessfor mobile communication to terminals, MS21 121 and MS31 131, located intheir own service coverage. In FIG. 1, wireless backhaul communicationbetween the HN 110 a and the RBNs, i.e., the RBN1 120 a and RBN2 130 a,may use the same or different frequency than that used for radio accesscommunication between the MBS 110 and MS11 111 or SBS1 120 and SBS2 130and MS21 121 and MS31 131. When the same frequency is in use, an antennafor wireless backhaul communication and an antenna for radio accesscommunication are rendered to use beams differently oriented, therebyminimizing interference. Further, according to the present disclosure,the wireless backhaul may be implemented based on mobile communicationradio access technology using beamforming antennas or based on wirelessLAN technology using beamforming antennas. According to an embodiment ofthe present disclosure, described is an example in which BS installed inHN is a MBS, and base station installed in RBN is an SBS, but thepresent disclosure may also apply to scenarios in which HN and RBN bothare installed in MBS or SBS. Further, the present disclosure may also beapplicable likewise where HN is connected to the network via a wiredbackhaul, as well as were HN is connected to the network by way ofanother wireless backhaul means.

According to an embodiment of the present disclosure, the wirelessbackhaul is operated to run in one of two operation states in order tomaximize wireless backhaul communication capacity and efficiency whileenabling RBN automated installation and operation. According to anembodiment of the present disclosure, the two operation states include abackhaul update state (BUS) and a backhaul optimum communication state(BOCS). The BUS and BOCS both support data communication of the wirelessbackhaul, but the BOCS offers a much higher communication efficiency.According to an embodiment of the present disclosure, an HN and RBNsconfiguring the wireless backhaul are operated in the same operationstate. In other words, when the HN is operated in the BUS, all of theRBNs connected to the HN to communicate are also operated in the BUS,whereas when the HN is operated in the BOCS, all the RBNs are operatedin the BOCS as well.

FIG. 2 illustrates an operation state transition of an HN according toan embodiment of the present disclosure.

Referring to FIG. 2, according to an embodiment of the presentdisclosure, an HN is operated in one of a BUS 220 and BOCS 240 accordingto predetermined operation transition conditions.

According to an embodiment of the present disclosure, a first condition(hereinafter, referred to as a BUS transition condition) for thewireless backhaul to transit from BOCS to BUS includes when the networkinstructs the HN to transit to the BUS to install a new RBN in thewireless backhaul or when the communication environment of the wirelessbackhaul already installed is varied to result in a decrease inperformance. The decrease in performance may include when the HNdetermines to transit to the BUS upon recognizing that a sharpperformance drop or link failure between the HN and RBN occurs, whenreceiving a request from an adjacent HN due to a deterioration ofperformance of the RBN connected with the adjacent HN, or when receivingan instruction for transition to BUS from the network. Additionally, theperformance decrease may also include when the network instructs atransition to BUS periodically or by the operator's instruction for aperformance enhancement in the wireless backhaul. In the case of RBN,there are included the situations where power is on, the link to RBNfails, or the serving HN connected with the RBN makes a state changeinto BUS. The above-enumerated BUS state transition conditions aredescribed below in further detail.

The wireless backhaul meeting such BUS transition conditions transitinto BUS and operate.

A first assumption is made, among others, to the scenario where a newRBN is installed in the wireless backhaul. According to an embodiment ofthe present disclosure, the wireless backhaul discovers an HN offeringthe optimal network connection to the new RBN and connects themtogether.

A next assumption comes into such a scenario that the communicationenvironment of the wireless backhaul already installed varies andreveals a performance down among the BUS transition conditions. Here,when the communication environment of the already installed wirelessbackhaul undergoes a variation and the wireless backhaul's resultantperformance drop encompasses scenarios in which backhaul communicationenvironments of pre-installed RBNs are subjected to a change resultingin a link failure with the serving HN used to be in linkage or a qualitydeterioration of existing link with the serving HN. According to anembodiment of the present disclosure, the wireless backhaul may discoveranother HN giving better communication than the HN presently linked withthe RBN does and alter serving HNs for the RBN. Or, the wirelessbackhaul may identify a communication path providing a bettercommunication performance for the same serving HN and change into theidentified communication path. In order to vary serving HNs or beams inserving HN, the HN repeatedly transmits a sync signal, common controlinformation and system information twice or more in directions or tolocations corresponding to all of the beams the HN provides. The HNfinds an optimal beam by conducting beam measurement and training on allof the HN's beams on downlink (DL) and uplink (UL). The HN receivesrandom access preamble or association request signal transmitted fromthe RBN through all the beams and supports a function of enabling a newRBN or RBN already in connection with other HN to link with the optimalHN. Further, the RBN conducts searching and scanning on all of the HN'sbeams while in BUS to detect signals transmitted from the HNs and doesbeam measurement and training on the HNs detected by all of the HNs' ownbeams on UL and DL to discover the optimal HN and the optimal beam withthe optimal HN. It sends a random access preamble or association requestsignal to the optimal HN and connects to the optimal HN.

According to an embodiment of the present disclosure, a BOCS transitioncondition of wireless backhaul includes when a new RBN is complete toinstall or a link-failed RBN successfully links to the network within apredetermined time. The condition also includes when the link-failed RBNfails to link with the network within the predetermined time or when aRBN subjected to a drastic link performance down makes link performancebetter by varying beams or serving HNs within a predetermined time. Alsoincluded is the scenario that the RBN drastically deteriorated in linkperformance fails to enhance link performance within the predeterminedtime, and a transition is made as per an instruction from the network.For RBN, such context is also included that the linked serving HNtransitions to BOCS.

The wireless backhaul, which meets the BOCS transition condition andthus operates in the BOCS, communicates using the optimaltransmission/reception beam and runs to maximize the efficiency andperformance of radio resources. For that purpose, according to anembodiment of the present disclosure, the HN operating in the BOCS sendssync signals to the HN's connected RBNs using partially limited beamsamong all of the HNs' own beams and communicates control information.According to an embodiment of the present disclosure, no operation issupported for the HN to discover the optimal beam while in the BOCS, andif necessary, beam measurement and training are restrictively carriedout on only some beams positioned adjacent to the optimal beamdiscovered in the BUS, thereby updating and tracking the optimal beam.The HN does not allow random access for access to a new RBN orcommunication of association request signals while in BOCS and does notback up access to the HN of the new RBN or RBN connecting with anadjacent HN.

According to an embodiment of the present disclosure, the RBN does notconduct search or scan for discovering a new serving HN while in theBOCS nor does the RBN performs beam measurement and training fordiscovering the optimal beam for all the RBN's beams. If necessary, beammeasurement and training are limitedly done on some beams adjacent tothe optimal beam discovered in the BUS, thereby updating and trackingbeams. No procedure (i.e., random access or transmission of anassociation signal) for accessing the adjacent HN is performed.

FIG. 3 illustrates a state transition of a RBN according to anembodiment of the present disclosure.

Referring to FIG. 3, according to an embodiment of the presentdisclosure, the RBN, when powering on in operation 310, transitions tothe BUS in operation 320. When meeting the BOCS transition conditionwhile operating in the BUS, the RBN transitions to the BOCS in operation340. Likewise, upon identifying that the RBN operating in the BOCS meetsthe BUS transition condition, the RBN transitions back to the BUS.

According to an embodiment of the present disclosure, the RBN mayoperate in three communication modes to support the optimalcommunication in the BOCS. Here, the three communication modescorrespond to a fixed beam mode (FBM), an adaptive beam mode (ABM), or alow duty mode (LDM). As set forth above, according to an embodiment ofthe present disclosure, while the HN and RBNs connected with the HN,which configure the wireless backhaul, are operated in the same manner,no separate limitation is imposed on communication mode of RBN operatingin the BOCS. Accordingly, a plurality of RBNs connected with the same HNmay operate in the same or different communication modes while operatingin the BOCS.

According to an embodiment of the present disclosure, in the FBM, HN andRBN communicate using a fixed optimal transmission/reception beam. Thus,the FBM may reduce waste of radio resources for discovering the optimalbeam, leading to a maximized use efficiency of radio resources.

When HN and RBN communicate using a fixed beam as in the FBM, theantennas of HN or RBN may be vibrated by an influence from the externalenvironment, such as strong wind gust, while in communication, resultingin performance deterioration. According to an embodiment of the presentdisclosure, HN or RBN in the ABM limitedly conducts beam measurement andtraining although using the same frame structure as that used in theFBM. As such, beam measurement and training are limitedly performed onsome beams adjacent to the fixed optimal beam, thereby enabling use ofthe optimal beam updated considering external environment.

However, wireless backhaul communication environments, mostly, are notaffected a lot by external environment and requiring operating in theABM is infrequent. Thus, according to an embodiment of the presentdisclosure, the wireless backhaul in the BOCS may have a defaultcommunication mode set to basically operate in the FBM 342 as shown inFIG. 3. Upon determining that a beam change is required due to, e.g.,influence from external environment, the wireless backhaul transitionsand operates in the ABM 344. When it is identified that there is noinfluence from external environment, the wireless backhaul transitionsand operates in the FBM 342. Lastly, when there is no terminal linked toa BS installed in the RBN or an active terminal is among terminalslinked to the BS, the BS may transition and operate in the LDM 346 wheresignal communication is minimized. In such case, the RBN may alsotransition to the LDM, minimizing the RBN's power consumption andinterference with other wireless backhaul. When recognizing the casewhere normal communication needs to be performed for the BS in the LDM346, a switch may be made into the FBM 342 or AMB 346 and wirelessbackhaul communication may be carried out. Here, specific conditions forswitching into each communication mode are described below in detail.The RBN operating in the LDM according to the present disclosure sendsbackhaul alive (BA) bits or information to the RBN's serving HN at aperiod previously agreed to, thereby periodically reminding the servingHN that the wireless backhaul link is not disconnected but alive.Accordingly, the HN identifies the reception of BA bits or informationat each period for the RBN operating in the LDM. When the result ofidentification reveals that no BA bit or information is received fromthe RBN at the period, it may be identified that a link failure occurson the RBN, and the wireless backhaul may be swiftly restored for thedisconnected link.

FIG. 4 illustrates an example of a frame structure according to anembodiment of the present disclosure, wherein according to an embodimentof the present disclosure, the exemplified frame structure is one usedfor cellular mobile communication, for ease of description.

For example, it is assumed that according to an embodiment of thepresent disclosure, HN and RBN each send and receive signals throughframes having a fixed size through beamforming. In such case, the frameincludes multiple subframes with a fixed length. Each of the multiplesubframes includes multiple slots with a fixed length, and one slotincludes multiple symbols. Referring to FIG. 4, for example, the frame400 includes five subframes, and one subframe 402 includes 20 slots. Oneslot may have a different number of symbols and a different structuredepending on the slot's type. For example, assuming that the frame 400is 5 ms long, one subframe 402 is 1 ms long, and one slot is 50 us long.The number and structure of symbols constituting one slot may be varieddepending on the type of slot. In the embodiment shown in FIG. 4, a type1 slot 404 a includes ten 5 us-long symbols constituted of a 4 us-longinformation interval and a 1 us-long cyclic prefix (CP) or protectioninterval. A type 2 slot 404 b includes eleven symbols each of which hasthe same length of information interval, 4 us. However, symbol 0 is 5 uslong, and the symbol 0's CP is 1 us long. Symbols 1 to 10 all are 4.5 uslong and their CP is 0.5 us long. A type 3 slot 404 c includes 25symbols, each being 2 us long, without a CP. A type 4 slot 404 dincludes 6.25 symbols, each being 8 us long, without a CP. Whenreceiving symbols including CPs during downlink and uplinkcommunication, HN and RBN receive only information intervals except theCPs.

According to an embodiment of the present disclosure, a frame on DLwhere HN sends a signal to RBN as shown in FIG. 4 may distinctivelyinclude an SS and BCH slot for transmitting a synchronization signal(SS) and shared control information (e.g., broadcast channel (BCH)), abeam measurement (BM) slot, a control slot, and a data slot. Further,the frame on UL where RBN sends a signal to HN may distinctively includea random access channel (RACH) slot, a BM slot, a control slot, and adata slot. Here, although the size of subframe and slot remainsunchanged, the number and combination of slots selected to constituteone subframe may be varied by communication environments, such as thenumber of antennas of HN and RBN, the number of beams of the antennas,and the number of RBNs. It is now assumed that according to anembodiment of the present disclosure each frame includes at least one SSand BCH slot and at least one downlink control slot.

According to an embodiment of the present disclosure, the framestructure may support frequency division duplex (FDD) schemes in whichDL and UL communication is simultaneously performed at differentfrequencies, respectively, as well as time division duplex (TDD) schemesin which the same frequency but different time slots are used. AlthoughFDD schemes have the same frame structure for both DL and UL, the FDDschemes may have different selections and combinations of slotsconstituting the frame. For example, TDD schemes may assign some slotsin each subframe in the given frame structure to DL communication andthe remaining slots to UL communication and may designate one or twoslots, as a protection interval, during a transmission-reception switchbetween DL and UL. As a specific example, slots 0 through 11 may beassigned to DL communication, and slots 13 through 19 to ULcommunication, and slot 12 may be set aside as a protection interval.

FIG. 5 illustrates an example of configuring an SS and BCH in a frameaccording to an embodiment of the present disclosure.

Referring to FIG. 5, according to an embodiment of the presentdisclosure, the SS and BCH slot are positioned in areas designated asminimum units for transmitting SS and BCH in one slot 500 having a fixedlength constituting a frame. Here, in order for the transmitting end tobe able to receive SS and shared control information, the SS and sharedcontrol information are repeatedly transmitted per antenna beam in theSS and BCH slot. For example, when slot 1 in subframe 0 of FIG. 4 is theSS and BCH slot, the transmitting end transmits SS and shared controlinformation in a fixed way in slot 1 of subframe 0 included in eachframe. Here, when the transmitting end comes up with a total of fivebeams, SS and shared control information in beam [0] using symbols 0 and1, SS and shared control information in beam [1] using symbols 2 and 3,and SS and shared control information in beam [2] using symbols 4 and 5are repeatedly sent. In order for the receiving end to identify whatnumber of transmission repetition SS and shared control information isreceived at, information indicating the number of transmissions may beincluded and transmitted in either the SS or shared control information.Here, the number of SS and BCH slots may be configured to correspondwith the number of transmission beams owned by the transmitting end. Itis assumed that while the number of SS and BCH slots in a frame may bevariably configured, the position of the first slot at which the SSstarts to be sent is fixed in the frame, and the SS and BCH slots areconsecutively present. For example, it is assumed that SS and sharedcontrol information are intended to be sent using ten transmissionbeams. In such scenario, two slots, i.e., slots 1 and 2, may be allottedas the SS and BCH slots in subframe 0. Further, when HN further narrowsbeam width and increases the number of beams in order to obtain a higherbeam gain, the HN needs to repeatedly send SS and BCH slotscorresponding to the increased number of beams. For example, when HNuses 60 transmission beams, SS and BCH slots need to be transmittedtwelve times.

FIGS. 6a and 6b illustrate examples of configuring a DL control slot andUL control slot in a frame according to an embodiment of the presentdisclosure.

Referring to FIG. 6a , according to an embodiment of the presentdisclosure, the DL control slot and UL control slot each are positionedin an area designated as a minimum unit for transmitting DL controlinformation in one slot having a fixed length constituting a frame. Forexample, the DL control slot is positioned in an area designated as aminimum unit in a slot 600, and the UL control slot is positioned in anarea designated as a minimum area in a slot 610. In the FDD scheme, slot0 in each subframe may be designated as DL control slot and UL controlslot, and in the TDD scheme, slot 0 in each subframe may be designatedas DL control slot, and slot 13 as UL control slot. In the above DL/ULcontrol slots, each symbol may be allotted for a different RBN thanthose of the other symbols in the control slot, and HN may use adifferent DL transmission beam or UL reception beam at each symbol.Specifically, in the embodiment shown in FIG. 6, ten symbols may betransmitted in one control slot 600, thereby enabling transmission ofcontrol symbols with up to ten HN beams. In FIG. 6a , HN sequentiallysends the ten symbols constituting the DL control slot through up to tentransmission beams. Each RBN receives all the symbols of the DL controlslot through the optimal reception beam and receives control informationfor each RBN among all the symbols of the DL control slot. Further, inFIG. 6b , HN sequentially receives the ten symbols of the UL controlslot through up to ten reception beams, and each RBN sends a UL controlsymbol to HN using each RBN's optimal transmission beam at a timecorresponding to the symbol assigned to the RBN.

FIG. 7 illustrates an example of configuring a DL and UL data slot in aframe according to an embodiment of the present disclosure.

Referring to FIG. 7, according to an embodiment of the presentdisclosure, an example is shown in which eleven symbols are transmittedand received through one slot 700 having a fixed length constituting aframe in order to raise transmission efficiency in DL/UL data slots.According to another embodiment, ten symbols may also be used throughthe slot 700. According to an embodiment of the present disclosure, HNand RBN do not change beams upon transmission or reception of symbols intheir respective corresponding data slots and the HN and RBN may changebeams only at the moment that a slot begins. HN and RBN, upon receptionof a corresponding data slot, eliminate the CP from each symbol whilereceiving the information interval of signal, thereby receiving data.

FIG. 8 illustrates an example of configuring a BM slot in a frameaccording to an embodiment of the present disclosure.

Referring to FIG. 8, an embodiment of configuring a BM slot is shown inwhich symbols each being 2 us long and without CP are repeatedlytransmitted in one slot 800 having a fixed length and constituting eachframe. On DL, HN sends the BM slot of FIG. 8 in fixed transmissionbeams, and RBN switches reception beams, e.g., in 2.5 us-long units. RBNassigns the foremost 0.5 us interval 802 as a protection interval forbeam switching while receiving the remaining 2 us-long signal to measurethe power of the transmission/reception beam combination. Further, thesame HN may form a plurality of beams with a plurality of antennas tosimultaneously transmit a plurality of BM signals, and the same HN'sother neighbor HNs may also transmit BM slots in the BUS at the sametime. In such case, RBN may be able to receive, without interference,the BM signals simultaneously transmitted from the plurality of HNs andthe antennas of the HNs. In particular, when the multiple neighbor HNsare not temporally synced with each other or have different distancesfrom RBN and resultantly different propagation times, the multiple BMslots received by RBN may fail to sync and cause interference. In orderto prevent such interference, according to an embodiment of the presentdisclosure, RBN may exclude the head 802 and the 2.5 us end 804 of theBM slot from use in BM like in the embodiment shown in FIG. 8. As aresult, in the FIG. 8 embodiment, measurement may be made on onetransmission beam and 18 reception beams. On DL, HN repeatedly sends theBL slot while sequentially switching the transmission beams for all theHN's transmission beams. Thus, when on DL HN has NHN transmission beams,and RBN has NRBN reception beams, completion of one-time BM for alltransmission/reception beam combinations with the BL slot shown in FIG.8 requires NHN [NRBN/18]up BM slots. Here, [X]up denotes a minimum oneamong natural numbers equal or larger than X. For example, when HN andRBN each have 60 beams, transmission/reception of 60*[60/18]up=60*4=240BM slots is required to perform one-time measurement on alltransmission/reception beam combinations.

In the case of UL BM, RBN sends BL slot in fixed beams, and HN receivessignals while switching reception beams as shown in FIG. 8, therebymeasuring receive power on transmission/reception beam combination. Insuch case, HN may be able to receive, without interference, the BMsignals simultaneously transmitted from the plurality of RBNs and theantennas of the RBNs. The same principle detailed above for DL BMapplies to UL BM, and no further description is given. Further, it mayalso be possible in UL BM to measure beams by receiving BM slot in fixedbeams while switching transmission beams in the slot, rather thantransmitting BM slot in fixed beams and switching reception beams in theslot.

FIG. 9 illustrates an example of configuring a UL RACH slot in a frameaccording to an embodiment of the present disclosure.

FIG. 9 shows an embodiment of configuring a RACH slot, in which RACHpreamble symbols each being 8 us long and without CP are repeatedlytransmitted 6.25 times in one slot 900 having a fixed lengthconstituting a frame. On UL, RBN sends the RACH slot using fixedtransmission beams. On UL, HN may repeatedly detect RACH frame signalswhile varying reception beams, e.g., four times, as shown in FIG. 9. HNreceives the RACH slot in beam [0] and uses the 8 us+2.5 us=10.5 us head902 of the RACH slot as a protection interval without detecting signaland detects the RACH preamble for the next 8 us-long signal. HN thenswitches the reception beam into beam [1] and receives an 8 us-longsignal after the 2.5 us-long protection interval to detect the RACHpreamble. Likewise, HN sequentially switches the reception beam intobeam [2] and beam [3] and receives an 8 us-long signal subsequent to the2.5 us-long protection interval in each beam to detect the RACHpreamble. According to an embodiment of the present disclosure, HN maydetect a round trip delay up to 8 us through the RACH slot structure andestablish a UL frame sync for RBNs located within a distance up to 1.2km. In the embodiment shown in FIG. 9, the RACH slot does not back upRACH signal detection for four HN reception beams in each slot. Thus, inorder to detect a RACH signal with more reception beams, more RACH slotsas much may be allocated. For example, when HN detects a RACH signalwith 60 reception beams, 15 RACH slots may be allocated.

According to an embodiment of the present disclosure, HN and RBN mayconduct wireless backhaul communication using slots in a frame asconfigured above. According to an embodiment of the present disclosure,various combinations may be possible for the above-described slotsdepending on antennas and beam environments used by HN and RBN, numberof RBNs, radio channel state or other various communicationenvironments, or necessary communication functionality and capability.As such, in order to select different slot combinations according to theneed in frame, the frame structure sends control and system informationover several distinct stages. In order to communicate with HN, RBN mayfirst receive SS and BCH slot to establish synchronization and receiveshared control information. Here, the shared control informationcontains shared information that needs to be known to RBN to establishframe synchronization with HN and to receive signals. For example, theshared information may include information on the position or order ofshared control information symbol in frame, information on physicalidentifier and global identifier of HN, system frame number (SFN),information differentiating operation states (i.e., BUS or BOCS) of HN,number of SS and BCH slots per frame, number of antennas used by HN,number of beams per antenna of HN, duplex information such as TDD orFDD, or signal bandwidth information.

According to an embodiment of the present disclosure, the DL/UL controlslot may contain physical layer control information and other shortcontrol information necessary for HN to conduct DL and UL wirelesscommunication with RBN. For example, such information may include radioresource allocation-related information on data or data slotscommunicated between HN and each RBN, such as physical downlink controlchannel (PDCCH) set forth in 3GPP LTE standards, modulation and codescheme (MCS) information, information on antennas and antenna techniquesused by HN, power control information, paging-related information, andRACH-related information. Further, as information corresponding to 3GPPLTE physical control format indicator channel (PCFICH), information onthe number of DL/UL control slots allotted to each subframe in the framemay be included as well. Further, as UL physical control informationnecessary for communication between HN and RBN, such as 3GPP LTEphysical uplink control channel (PUCCH), channel state information(CSI), hybrid automatic repeat request (ARQ) Ack/Nack information, andscheduling request (SR) information may also be included. Further, otheradditional short control information may be included, such asinformation on transmission/reception beam being used or which to beswitched into by HN and RBN, or information (backhaul status information(BSI)) indicating the status of wireless backhaul of RBN operating inLDM of BOCS, or other short control information for HN to controlwireless communication of RBN.

According to an embodiment of the present disclosure, the DL/UL dataslot includes data transferred between HN and RBN through DL and ULwireless communication. In other words, all user data and controlinformation communicated between BS installed in RBN and network throughHN are transmitted and received in data slots. Various higher layercontrol information between HN and RBN which are necessary for wirelesscommunication between HN and RBN may also be included. Further, the dataslot may include various system information (SI) that needs to be knownfor RBN to access and communicate with HN. For example, included areinformation corresponding to various SI defined in 3GPP LTE standards,detailed information on DL and UL BM and use of beams, and other systeminformation necessary for operating in BUS or BOCS.

The following Table 1 represents slots, signals, or informationtransmitted and received in the BUS and BOCS when HN and RBNconstituting a wireless backhaul according to the present disclosureperform wireless backhaul communication using the frame architecturesdescribed above in connection with FIGS. 4 to 9.

Table 1 shows signals and information communicated in communication modeand operation state of wireless backhaul according to an embodiment ofthe present disclosure

TABLE 1 Operation Operation mode (BOCS) Slot/signal/information modeCommunication Communication Communication types (BUS) mode (FBM) mode(ABM) mode (LDM) DL SS/BCH slot full Optimal beam Optimal beam Optimalbeam & coverage scheduling UL RACH slot full X X X coverage DL/UL BMslot Full X Limited X DL/UL control slot ◯ ◯ ◯ Scheduling DL/UL dataslot ◯ ◯ ◯ X

Table 2 below represents various operations and functions supported bywireless backhaul in the BUS and BOCS according to an embodiment of thepresent disclosure.

TABLE 2 Operation mode (BOCS) Operations and Operation modeCommunication Communication Communication functions (BUS) mode (FBM)mode (ABM) mode (LDM) HN searching ◯ X X X Network ◯ X X Xentry/handover Beam training Full X Limited X control informationBroadcast/dedicated Dedicated Dedicated Scheduling & dedicated Data ◯ ◯◯ ◯

Referring to Table 1 above, according to an embodiment of the presentdisclosure, HN and RBN constituting a wireless backhaul, when operatingin the BUS, uses all of the frame including an SS and BCH slot, UL RACHslot, DL/UL BM slot, DL/UL control slot, and data slot and supports allfunctions for mobile communication between a BS and MS on a mobilecommunication system. HN operating in the BUS sends the DL SS and BCHslot for the HN's full coverage for RBNs to sync with the HN at allpositions in the HN's coverage and receives HN's shared controlinformation and system information. Here, HN includes and transmits, inthe shared control information, information indicating that the HN'soperation mode is the BUS. Since HN uses a narrow beam, the HNrepeatedly sends the signal while varying transmission beams in order tosend the signal for the HN's full communication coverage. RBN operatingin the BUS receives neighbor HNs' SS and shared control information aswell as that of the RBN's serving HN and performs searching and scanningon HN to discover an HN providing the optimal communication quality.

Further, HN operating in the BUS receives the UL RACH slot assigned forall of the RBNs positioned in the HN's coverage to establish ULsynchronization with the HN and perform UL communication. HN repeatedlyassigns RACH slots while switching reception beams and receives signalsfrom a corresponding RBN in order to receive RACH slot regardless of theposition of RBN located in the HN's coverage. Referring to Table 2, HNreceives, in the BUS, RACH signals from a RBN positioned in a neighborHN and a new RBN as well as a RBN positioned in the HN's coverage tosupport UL sync, network entry (attach), and handover. RBN operating inthe BUS may send a RACH signal to the serving HN to establish a UL syncand sends a RACH signal to a neighbor HN, rather than the RBN servingHN, to link or hand over to the neighbor HN.

As shown in Table 1 above, HN and RBN operating in the BUS conduct BMand training on all transmission/reception beam combinations on DL andUL to select the optimal transmission/reception beam combination on DLand UL each. Based on the BM result of selecting the optimaltransmission/reception beam combination, each RBN may determine theoptimal HN offering the optimal service quality to the RBN. For example,assuming that HN and RBN each uses 60 beams, one-time BM on DL and ULfor all transmission/reception beam combinations requires60*[60/18]up=60*4=240 BM slots. Here, since wireless backhaulcommunication is done when HN and RBN both are located stationary, thetime restriction for completing BM is not that strict unlike on mobilecommunication. Thus, e.g., when one slot is allocated per subframeconstituting a frame for BM on DL and UL, one time of BM may be done ata time of 240 subframes, i.e., 240 ms. When HN sends SS and BCH slotwith 60 transmission beams, 12 DLs lots need to be assigned for SS andBCH slot per frame. From above, it can be seen that significant waste ofradio resources occurs. Here, waste of radio resources may be reduced bydecreasing the number of beams used for the SS and BCH slots, but RBNmay fail to communicate with HN due to a sync failure. Further,reception of 60 beams for RACH slot requires 15 uplink RACH slots to beallocated.

SI of a new HN is needed for RBN operating in the BUS to access andcommunicate with the new HN. Such SI is transmitted through the DL/ULdata slot. Accordingly, a corresponding RBN may be able to receive theSI in the full coverage regardless of the position of the RBN located inthe HN coverage as the HN does on shared control information. Thus,although data is transmitted using a fixed transmission beam in theDL/UL data slot, when SI is included as shown in Table 1, transmissionbeams provided to be sent in the full coverage are switched andrepeatedly transmitted. Likewise, since radio resource allocationinformation on the SI maybe transmitted in the full coverage of HN, theDL/UL control slot containing the radio resource allocation informationswitches and repeatedly transmits transmission beams provided to betransmitted in the full coverage.

Referring to Table 1 above, according to an embodiment of the presentdisclosure, when the wireless backhaul is operated in the BOCS, HN andRBN supports only some of the functions supported by the mobilecommunication system. Accordingly, HN and RBN operating in the BOCS eachuse the optimal beam for transmission/reception of UL/DL control slotand data slot. Further, upon transmission of DL SS and BCH slot, HN doesnot broadcast in the HN's full coverage but sends them to only RBNscurrently linked thereto. As possible, the HN sends signals with aminimum number of beams. Further, HN operating in the BOCS sends theHN's SI to a corresponding RBN only once or when required. Referring toTable 2 above, RBN operating in the BOCS receives the sync signal fromonly serving HN but not from neighbor HN. Nor does the RBN performsearching and scanning on neighbor HN.

Referring to Table 1, according to an embodiment of the presentdisclosure, when the wireless backhaul operates in the BOCS, thewireless backhaul does not support UL RACH transmission/reception andthus does not assign a UL RACH slot. Referring to Table 2, HN operatingin the BOCS does not support handover or access for new RBNs or RBNsbelonging to a neighbor HN nor does the HN support RACHtransmission/reception for RBNs linked thereto. Likewise, RBN operatingin the BOCS does not send a RACH signal for updating UL sync with theserving HN and does not send RACH signals to neighbor HNs. Further, theRBN does not support DL and UL measurement and training on all of thebeams of HN and RBN. Nor does the RBN support BM and training onneighbor HNs. As shown in Table 1, no BM slot is assigned to RBNsoperating in the FBM and LDM of the BOCS, and BM and training are notsupported. However, RBN operating in the ABM conducts limited BM andadaptation using some candidate beams adjacent to the optimaltransmission/reception beam discovered in the BUS for the serving HN. HNand RBN operating in the FBM and ARM of the BOCS communicate data andcontrol information using the optimal beam to provide wireless backhaulcommunication, and HN and RBN operating in the LDM communicate controlinformation at a time previously agreed on. Further, HN sends a syncsignal to RBN operating in the LDM only at times previously agreed on,and RBN operating in the LDM abstains from transmission/reception ofdata slot.

FIGS. 10 to 12 illustrate examples of frame structures according tooperation modes of wireless backhaul according to embodiments of thepresent disclosure. For ease of description, it is assumed that, basedon a TDD scheme, a total of 12 slots, i.e., slot 0 through slot 11, areallocated to DL communication in each subframe, and a total of sevenslots, i.e., slot 13 through slot 19, are allocated to UL communication.Slot 12 is assigned as a protection interval. Thus, a total of 60 slotsand a total of 35 slots are assigned to DL and UL, respectively, perframe through the five subframes.

FIG. 10 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated as BUSs according to an embodiment of thepresent disclosure.

Referring to FIG. 10, HN operating in the BUS assigns slot 0 and slot 13to DL and UL control slot, respectively, per subframe, as an example.For example, assuming that HN transmits SS and BCH symbols using 60beams, a total of 12 slots are needed. To that end, in the embodimentshown in FIG. 10, a total of 12 slots are assigned as SS and BCH slotsthrough slots 1 to 3 of each of four subframes, i.e., subframes 0 to 3.Further, slot 4 in each subframe is assigned as a BM slot. HN sends BMslots while switching the HN's beams at a period of 12 frames eachconstituted of five subframes or 60 subframes corresponding to thenumber of the HN's beams. Here, when RBN performs BM measurement using60 reception beams, one time of BM requires 240 ms for alltransmission/reception beam combinations on DL.

Meanwhile, in the embodiment shown in FIG. 10, slot 18 in each subframeis assigned as a UL BM slot. Further, slot 19 in each subframe isassigned as a UL RACH slot. Here, assuming that HN detects RACH preamblewith four reception beams for one RACH slot, the HN may detect RACHpreamble using 20 reception beams per frame. Thus, HN needs a total ofthree frames to detect RACH preamble using 60 beams. As described abovein connection with Table 1, HN operating in the BUS, when sending SIthrough the DL data slot, repeatedly sends the DL data slot whileswitching the beams. Upon sending radio resource allocation informationon SI through DL control slot, the HN may repeatedly send the DL controlslot while switching the beams in the same way. The amount of SI to besent by HN may vary depending on system implementations. When estimatedbased on the embodiment shown in FIG. 10, it may be regarded for SI ofHN that data slot transmitted through slots 1 to 3 of subframe 4 areassigned for transmission of SI. Then, data slots used only for datacommunication in the embodiment of frame structure shown in FIG. 10include 35 slots on downlink and 20 slots on uplink for each frame.

FIG. 11 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated as BOCSs, and the communication mode isan FBM according to an embodiment of the present disclosure.

Referring to FIG. 11, HN and RBN operating in the FBM, both, are locatedat fixed positions, and communication channel remains substantiallyunchanged, and such environment thus requires a very small amount ofcontrol information. Accordingly, HN operating in FBM assigns, e.g.,slots 0 and 13 of subframe 0, as DL and UL uplink control slots,respectively, but does not assign control slots to the other subframesin the frame.

Further, since the FBM uses only fixed optimal beam between HN and RBNupon transmission of SS and BCH symbols, the number of slots requires isalso very small. Accordingly, in the embodiment shown in FIG. 11, SS andBCH slot are assigned to only slot 1 of subframe 0. Further, the FBMmakes no allocation of BM slot and UL RACH. Thus, in the frame structureaccording to the embodiment shown in FIG. 11, as data slots used purelyfor data transmission, a total of 58 slots on DL and a total of 34 slotson UL may be used in each frame. As compared with the embodiment shownin FIG. 10, it can be identified that performance of data transmissionis enhanced by about 65% and about 70% for DL and UL, respectively.

FIG. 12 illustrates a frame structure when an HN and RBN configuring awireless backhaul are operated as BOCSs, and the communication mode isan ABM according to an embodiment of the present disclosure.

Referring to FIG. 12, the ABM performs DL/UL BM that is not done in theFBM. DL/UL BM performed in the AMB is limited for some adjacent beams ofthe optimal beam determined in the BUS, and thus, it may be conductedmore rapidly as compared with the BM period of BUS. For example, it isassumed that HN operating in the ABM conducts BM on five candidate beamswith the existing optimal beam selected for each of four RBNs. In suchcase, HN performs BM on a total of 4×5=20 candidate beams. Further, itis assumed for RBN that BM is measured on nine candidate beams with theexisting optimal beam selected, for example. In such case, DL beammeasurement period for HN is reduced to 20*[9/18]_(up)=20*1=20 ms.Assuming that BM is simultaneously performed on UL for each of the fourRBNs, BM period is down to 9*[20/18]_(up)=9*2=18 ms, and when BM issequentially measured on the four RBNs, the period is down to4*9*[5/18]_(up)=4*9*1=36 ms. When the BM measurement period isunnecessarily short as compared with the antenna vibration speed,resource waste may be reduced by decreasing the number of BM slots andincreasing the BM period. For example, in the embodiment shown in FIG.12, only one slot, as BM slot, is assigned per subframe. Accordingly,four more slots may be utilized as data slots per frame, leading toincreased efficiency. Although BM period is increased to 100 ms, 90 ms,and 180 ms, which are five times as much as that when four slots come inuse, a much shorter time may be taken as compared with the BM period inthe BUS, i.e., 240 ms. According to another embodiment, when HNoperating in the BOCS conducts wireless backhaul communication withmultiple RBNs, and BM is required only for HN and some RBNs, HN sends orreceives BM slot for the RBNs requiring BM in fixed beams, and only RBNswhich are intended to do BM, do so.

According to another embodiment, when HN operating in the BOCS conductswireless backhaul communication with multiple RBNs, and HN alonerequires BM but the RBNs don't, HN sends or receives BM slot to the RBNsto perform BM, and the RBNs receive or send the BM slot in fixed beamsto support HN for BM.

According to another embodiment, when HN operating in the BOCS carriesout wireless backhaul communication with multiple RBNs, and at least oneof the RBNs is in the LDM communication mode, HN sends SS and BCH symbolfor the at least one RBN at a time previously agreed on with the atleast one RBN and sends and receives DU/UL control slot symbols. HNcommunicates signals with RBNs, which are not in the LDM communicationmode, using a frame structure as illustrated in FIG. 11 or 12, accordingto the communication mode of the RBNs. HN does not communicate data slotand BM slot with the at least one RBN operating in the LDM. Further, theat least one RBN operating in the LDM sends BA bit or information to theserving HN in UL control slot at a previously agreed period toperiodically remind the serving HN that the wireless backhaul link isnot disconnected but remains alive.

FIG. 13 illustrates an example of an applicable beacon interval (BI)structure according to an embodiment of the present disclosure.

BI in FIG. 13 shows an example of a BI structure as used in IEEE802.11ad. The IEEE 802.11ad standard defines wireless LAN communicationbetween directional multi-gigabit (DMB) stations (STAs) communicatingsignals using beamforming antenna at a high frequency, e.g., 60 GHz, andchannel access in BI units. Referring to FIG. 13, a BI includes a beaconheader interval (BHI) and a data transfer interval (DTI). The BTIincludes a beacon transmission interval (BTI), association beamformingtraining (A-BFT) interval, and announcement transmission interval (ATI).The DTI includes one or more contention-based access periods (CBAPs) andscheduled service period (SP). Personal basic service set control point(PCP)/access point (AP) STA assigns a BI and provides BI allocationinformation to non-PCP/non-AP STA. BTI is an access interval duringwhich PCP/AP STA sends at least one DMG beacon frame to non-PCP/non-APSTA. Here, beacon frames not only provide a network sync to STA but alsotransfers BI allocation information, DMG capability information, andinformation corresponding to the shared control information and SI ofmobile communication. A-BFT is an interval during which STAs select theoptimal beam by performing beamforming training. ATI exchanges a requestframe and response frame for access management on a one-to-one basiswith PCP/AP STA or non-PCP/non-AP STA to offer association anddisassociation of STA, send a request for service period, or transferscheduling information. In CBAP of DTI, all STAs have a chance of randomdata transmission in a carrier sense multiple access with collisionavoidance (CSMA/CA) scheme, and in SP, STAs transmits data in a timedivision multiple access (TDMA) scheme according to PCP or AP'sscheduling.

The above-described IEEE 802.11ad standard may be used to implement awireless backhaul according to an embodiment of the present disclosure.In this case, the following Table 3 represents access intervalssupported in the BUS and BOCS when HN and RBN constituting a wirelessbackhaul according to the present disclosure conduct wireless backhaulcommunication based on the IEEE 802.11ad standard, and Table 4represents operations and functions supported by the wireless backhaulaccording to the present disclosure.

TABLE 3 Operation mode (BOCS) Operation mode Communication CommunicationCommunication BI (BUS) mode (FBM) mode (ABM) mode (LBM) BTI fullcoverage Optimal beam Optimal beam Optimal beam A-BFT ◯ X X X ATI ◯Optimal beam Optimal beam Scheduling DTI CSAB ◯ X X X DTI SP ◯ ◯ ◯ X

TABLE 4 Operation mode (BOCS) Operations and Operation modeCommunication Communication Communication functions (BUS) mode (FBM)mode (ABM) mode (LBM) Scan ◯ X X X Association/change ◯ X X X HN Beamtraining Full X Limited X Control Broadcast/dedicated DedicatedDedicated Scheduling & dedicated Data CSMA/TDMA TDMA TDMA X

Referring to Table 3 above, according to an embodiment of the presentdisclosure, when wireless backhaul operates in the BUS, the wirelessbackhaul may support all access intervals as per the IEEE 802.11adstandard and all wireless LAN functionality as per the IEEE 802.11adstandard. According to an embodiment of the present disclosure, wirelessbackhaul may additionally provide operation mode indication informationindicating that the operation mode of wireless backhaul is the BUS inthe DMB beacon frame. HN operating in the BUS sends DMG beacon frameusing the beams of all the HN's antennas during BTI and providessynchronization to RBNs intended to access the HN. Further, RBNoperating in the BUS receives DMB beacon frame and performs HN scanningbased on the DMB beacon frame. Further, the RBN may support sector levelsweep (SLS) beam training between HN and RBN using BTI and A-BFTintervals to select the optimal sector beam. Additionally, the RBN mayperform beam refinement protocol (BRP) to select the optimal receptionsector beam or may select a more accurate optimal transmission/receptionbeam through more precise beam training. BRP setup for performing BRPmay be done during ATI or DTI, and BRP beam training may be done duringDTI. During ATI, HN and RBN exchange a request frame and response framefor access management on a one-to-one basis to offer association anddisassociation of STA, send a request for service period, or transferscheduling information. During CBAP of DTI, all the RBNs have a changeof data transmission in a CSMA/CA scheme. Further, during SP of DTI, HNsends data to RBN in a TDMA scheme or each RBN sends data to HN during adesignated SP interval in a TDMA scheme in response to HN's instruction.DTI scheduling information is transmitted from HN to RBNs in theannounce frame of ATI or DMG beacon frame of BTI. As a result, in thewireless backhaul according to an embodiment of the present disclosure,RBN operating in the BUS may scan HNs, search for a new HN offering theoptimal service quality to the RBN, connect with the searched new HN orchange the serving HN into the new HN. All the beams may be used tosupport beam training to discover and select the optimaltransmission/reception sector beam and detailed beam for wirelessbackhaul communication between HN and RBN, and control information anddata of HN and RBN may be communicated in the CSMA/CA scheme and TDMAscheme.

Referring to Table 3 above, when the wireless backhaul according to anembodiment of the present disclosure operates in the BOCS, only some ofthe functions provided in the IEEE 802.11ad wireless LAN standard aresupported. Also in such case, HN may additionally send operation modeindication information indicating that the HN's operation mode is theBOCS through DMB beacon frame. According to an embodiment of the presentdisclosure, HN sends DMG beacon frame of BTI to only RBNs alreadyconnected in the BOCS, and in this case, limits the number of times oftransmission to the minimum using the optimal transmission beamdetermined in the BUS. Referring to Table 3 above, according to anembodiment of the present disclosure, when the wireless backhauloperates in the BOCS, no A-BFT interval is allocated, and ATI intervalis limited to the minimum. Further, in the BOCS, no DTI CBAP is assignedwhile only SP is assigned. Referring to Table 4 above, the BOCS doesneither support SLS beam training nor BRP beam training. However, uponoperating in the ABM of BOCS, beam tracking is supported of conductingbeam training on some candidate beams adjacent to the optimal beamalready selected during the DTI interval. Further, according to anembodiment of the present disclosure, such a LDM is supported where apower save mode is operated in which RBN operating in the BOCS wakes upat a pre-agreed time and does not communicate signals at other times. Asset forth above in Table 2, RBN operating in the BOCS does not scan HNand does not support connection to a new HN or change of serving HN.Further, the ABM provides limited beam training support and thussupports beam tracking, a type of beam training for varying orre-discovering the sector beams of HN and RBN and detailed beam of thesector beam. Also in use of the IEEE 802.11ad standard, according to anembodiment of the present disclosure, the wireless backhaul operating inthe BOCS uses the optimal HN and optimal beam discovered in the BUS tocommunicate control information and data to minimize waste of accessinterval. Here, rather than the control information being broadcast inall the beams, information necessary for each RBN is communicated in theoptimal beam, and the data is communicated in a TDMA scheme byscheduling without support of CSMA/CA.

FIGS. 14 to 17 illustrate examples of beams used for communication ofslots, symbols, signals, or information according to the operation modeand communication mode which HN and RBN constituting a wireless backhaulaccording to the present disclosure have currently switched into.

FIG. 14 illustrates beams used for transmission and reception ofinformation and slots when HNs and RBNs configuring a wireless backhaulare operated as BUSs according to an embodiment of the presentdisclosure. Here, HN and RBN operating in the BUS use their ownrespective transmission/reception beams.

FIG. 14 illustrates an example in which HN3 uses all the beams uponcommunication with each of RBN 31 to RBN 34 located in the HN3'scoverage, and RBN 31 to RBN 34 also use all their beams forcommunication with HN3. Likewise, the remaining HNs and RBNs also useall their transmission beams to perform communication in the instantembodiment.

FIG. 15 illustrates beams used when HNs and RBNs configuring a wirelessbackhaul are operated in an FBM of a BOCS according to an embodiment ofthe present disclosure.

Referring to FIG. 15, RBN communicates with the RBN's optimal HN using afixed optimal beam. For example, RBN 44 communicates with the optimalHN, HN 4, using a fixed optimal transmission/reception beam. HN 4operating in the FBM of BOCS communicates with each of RBN 41 to RBN 43permitted to access HN 4 using the optimal transmission/reception beam.Likewise, the remaining HNs, i.e., HN 1 to HN 3, operating in the FBM ofBOCS also communicate with the RBNs permitted to access them using theoptimal transmission/reception beam. Accordingly, the backhaul operatingin the FBM of BOCS may increase communication capability by minimizinginterference and waste of radio resources.

FIG. 16 illustrates beams used when HNs and RBNs configuring a wirelessbackhaul are operated in an ABM of a BOCS according to an embodiment ofthe present disclosure.

According to an embodiment of the present disclosure, HN and RBNoperating in the ABM of BOCS, upon recognizing that beam training isrequired, sends or receives additional BM slot to discover the optimaltransmission or reception beam. Referring to FIG. 16, HN1 and RBN11 toRBN14 all perform beam training to discover the optimal beam. On thecontrary, while RBN21 to RBN23 conduct beam training, their serving HN,HN2, remains in the state of having beam fixed. In contrast, HN3discovers the optimal beam by performing beam training on each of RBN31to RBN33 currently connected while RBN31 to RBN33 remain with theirbeams fixed. While HN4 discovers the optimal beam by performing beamtraining on RBN41 and RBN43 among RBNs connected to HN4, RBN42 and RBN44are in the state of their beams being fixed. RBN41 and RBN42 discoverthe optimal beam by performing beam training whereas RBN43 and RBN44 arein the state where beams remain fixed.

FIG. 17 illustrates a result obtained through a wireless backhauloperated as a BUS according to an embodiment of the present disclosure.

Referring to FIG. 17, there is shown a state in which new RBNs, RBN24and RBN34, are installed in the existing wireless backhaul, as denotedin reference number 1700, and RBN 24 and RBN34 are connected with HN2and HN3, respectively. Reference number 1702 denotes an example in whichRBN12 recognizes that HN3 offers a higher communication quality thanserving HN1 linked and communicating with RBN12, disconnectscommunication with HN1, and changes serving HNs connecting to HN3.Likewise, reference number 1704 denotes an example in which RBN31recognizes that HN2 provides a higher communication quality than servingHN3 used to connect and communicated with RBN31 does, disconnectscommunication with HN3, and changes serving HNs connected with HN2.Regarding reference number 1706, it is assumed that there is areflecting object 1, e.g., a building or object, which present thoselarger than the LOS communication path and beam used by HN1 and RBN14upon communication. In such case, such a circumstance is shown where HN1and RBN14 each change the optimal beam into a beam corresponding to thedirection of reflecting object 1 by recognizing that the communicationquality of NLOS path where radio waves are reflected and received byreflecting object 1 is higher. Regarding reference number 1708, it islikewise assumed that there is another reflecting object 2, e.g., abuilding or object presenting those larger than the LOS communicationpath and beam used by HN4 and RBN44 upon communication. In such case,such a circumstance is shown where HN4 and RBN44 each change the optimalbeam into a beam corresponding to the direction of reflecting object 2by recognizing that the communication quality of path where radio wavesare reflected and received by reflecting object 2 is higher.

According to an embodiment of the present disclosure, HN and RBNoperating in the BUS perform beam training on all theirtransmission/reception beam combinations to select the optimal HN andthe optimal transmission/reception beam combination to be used forcommunication with the optimal HN for each RBN. Since beam training isperformed on all the transmission/reception beam combinations for suchpurpose, the time for beam training is very long, and waste of radioresources is increased. In contrast, according to an embodiment of thepresent disclosure, HN and RBN operating in the ABM of BOCS conductlimited beam training on only some adjacent beams using the optimal beamalready discovered during the BUS, so that the time required for beamtraining is reduced, and the amount of radio resources used isshortened. As a specific example, assuming that HN and RBN each uses atotal of 60 beams, HN and RBN operating in the BUS may perform beamtraining on 60×60=3600 beam combinations at each measurement period. Incomparison, under the assumption that HN and RBN operating in the ABMperforms beam training only on nine candidate beams, the total number ofbeam combinations for beam training is significantly reduced to 9×9=81.Beam training in the ABM may quickly discover the optimal beam whenthere is an influence from external environment. However, since beamtraining and selection of optimal beam in the ABM are limited to theexisting optimal communication path already discovered in the BUS, nochange in the beam direction corresponding to the change in thecommunication path occurs as in reference numbers 1706 and 17087 of FIG.17.

FIG. 18 illustrates an installation structure for a RAN and backhaulnode (BN) according to an embodiment of the present disclosure. Here, BNcorresponds to HN or RBN, and RAN corresponds to MBS or SBS.

Referring to FIG. 18, in the structure denoted in reference number1800A, a BN 1820A and a RAN 1840A are implemented as devices independentfrom each other and are respectively installed in different cases,boxes, housings, or racks. BN 1820A and RAN 1840A are connected witheach other via a connecting line or cable 1860A. Although in thestructure denoted in reference number 1800B a BN 1820A and a RAN 1840Bare implemented as devices independent from each other, the BN 1820A andthe RAN 1840B may be installed in a single shared case 1800B. In thestructure denoted in reference number 1800B, e.g., HN and BSrespectively are implemented as boards independent from each other,installed in the same rack, and connected together by way of abackplane. In the structure denoted in reference number 1800C, BN andRAN are implemented as a single device. For example, in the structuredenoted in reference number 1800C, RBN and BS are implemented on thesame board and are connected together via a bus.

FIG. 19 illustrates a structure of an antenna for radio access and anantenna for wireless backhaul according to an embodiment of the presentdisclosure.

Referring to FIG. 19, for example, in the antenna 1 structure 1900A, anantenna 1920A for wireless backhaul and an antenna 1940A for radioaccess are independently implemented and separately installed from eachother. The antenna 1 structure 1900A may be advantageous when somecharacteristics among antenna-related information including usefrequency, number of antennas and beams, antenna pattern or beampattern, and vertical or horizontal direction of antenna differ for theantenna 1920A for wireless backhaul and antenna 1940A for radio access.An antenna structure 2 1900B is a structure in which an antenna array1920B for wireless backhaul and an antenna array 1940B for radio accessare implemented on the same antenna hardware. In such case, antennaarrays 1920B and 1940B, despite being implemented on the same antennahardware, have different radio frequency (RF) elements connected withthe antenna arrays. In particular, in such case, the antenna arrays1920B and 1940B may have some characteristics (use frequency or numberand direction of antennas) designated to be the same and othercharacteristics (number of beams, beam pattern, and beam direction)designated to be different. An antenna structure 3 1900C is a structurein which beams 1922C and 1924C for wireless backhaul and beams 1942C and1944C for radio access are created through the same antenna hardware andarray. The antenna structure 3 1900C, albeit having the same antennahardware and array, have RF elements connected thereto implemented to beindependent from each other to generate different beams. In such case,substantially all of the characteristics of antennas and beams forwireless backhaul and radio access are the same while beams for wirelessbackhaul and beams for radio access may be selected differently fromeach other.

FIG. 20 illustrates an example of a radio access network where awireless backhaul is installed according to an embodiment of the presentdisclosure. Although the radio access network shown in FIG. 20illustrates an LTE RAN structure as an example, the present disclosuremay also be applicable to other communication networks to whichbeamforming may apply.

Referring to FIG. 20, according to an embodiment of the presentdisclosure, in the random access network 2000 where wireless backhaul isinstalled, a RBN 2002 is wirelessly connected to an HN 2004 to providenetwork connection to a RBN-BS which is a random access node of RBN.FIG. 20 illustrates an example in which the BSs respectively installedin the RBN and the HN are shown as single devices RBN-BS 2002 and HN-BS2004 without being separated from the RBN and HN. Thus, RBN and HNrespectively may hereinafter be denoted as RBN-BS 2002 and HN-BS 2004.

RBN-BS 2002 and HN-BS 2004 are connected together via a wirelessinterface Ub.

According to an embodiment of the present disclosure, wireless interfaceUb for wireless backhaul may use beamforming-based cellular mobilecommunication random access technology as described above in connectionwith FIGS. 4 to 12 or beamforming wireless LAN random access technologydefined in IEEE 802.11ad. Further, RBN-BS 2002 terminates S1 and X2interface for operation of BS connected thereto. HN-BS 2004 provides anS1 and X2 proxy function to RBN-BS 2002 and other network nodes, i.e.,another BS 2006, mobility management entity (MME)/serving gateway (S-GW)2008 and 2010. The S1 and X2 proxy function includes a function fordelivering S1 and X2 signaling messages for MS and a function fortransferring GTP data packets between the S1 and X2 interface related toRBN and S1 and X2 interface related to other network nodes. The proxyfunction enables HN-BS 2004 to play a role as a MME (with respect toS1-MME), adjacent BS (with respect to X2), or S-GW (with respect toS1-U). Further, HN-BS 2004 embeds and provides S-GW/pdn-gateway (P-GW)functions necessary for RBN operation on RBN-BS 2002. Specifically, TheHN-BS 2004 generates a session for RBN, manages a radio bearer for RBN,and terminates the S1 interface towards the MME serving RBN. Further,HN-BS 2004 performs data packet mapping and signaling to radio bearersset for RBN operation. Signaling and data packet mapping are conductedon radio bearers. HN-BS 2004 embeds the P-GW functionality of assigningan internet protocol (IP) address other than the S1 IP address of RBN-BS2002 to RBN-BS 2002 for operation and maintenance (OAM).

According to an embodiment of the present disclosure, the wirelessbackhaul provides a GTP tunnel in HN and RBN to deliver radio bearers ofMS located in the service coverage of BS installed in RBN. For the GTPtunnel, HN and RBN according to an embodiment of the present disclosuresupports an S1 and X2 user plane interface.

FIG. 22 illustrates an example of a S1 user plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure.FIG. 22 is a view illustrating an example of an X2 user plane protocolstack structure for supporting an operation of an HN and RBN configuringa wireless backhaul according to an embodiment of the presentdisclosure.

Referring to FIGS. 21 and 22, S1 and X2 user plane packets are mapped toradio bearers through a Ub interface.

The protocol stack of RBN includes, e.g., GTP, user datagram protocol(UDP), IP and packet data convergence protocol (PCDP)/radio link control(RLC)/medium access control (MAC)/physical layer (PHY). The protocolstack of S-GW includes GTP, UDP, IP, layer2 (L2), and L1. According toan embodiment of the present disclosure, HN has a stack structure wherethe protocol stack of RBN and the protocol stack of S-GW are mapped toprovide a connection with S-GW to RBN.

Further, embodiment of the present disclosure supports an S1 and X2control plane interface for controlling wireless backhaul. FIG. 23 is aview illustrating an example of an S1 control plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure.

Referring to FIG. 23, one S1 interface relation exists between each RBNand HN, and an S1 interface relation is present between each MMEincluded in MME pool and HN. HN processes and delivers all S1 messagesbetween RBN and MME for all UE-dedicated procedures. S1-AP messageprocessing includes varying S1-AP UE IDs, transport layer addresses, andGTP tunnel endpoint identifiers (TEIDs) and does not change otherportions in S1-AP message. Non-UE-dedicated S1-AP procedures areterminated in HN and are internally processed between RBN and HN andbetween HN and MME. Upon receiving non-UE-dedicated S1 message from MME,HN may trigger corresponding S1 non-UE-dedicated procedures for RBN.

Therefore, an example protocol stack of RBN includes S1-AP, streamcontrol transmission protocol (SCTP), IP, and PDCP/RLC/MAC/PHY. MMEincludes S1-AP, STCP, IP, L2, and L1. Likewise, HN providing connectionbetween MME and RBN has a stack structure in which the protocol stacksof RBN and MME are mapped.

FIG. 24 illustrates an example of an X2 control plane protocol stackstructure for supporting an operation of an HN and RBN configuring awireless backhaul according to an embodiment of the present disclosure.

Referring to FIG. 24, according to an embodiment of the presentdisclosure, there is one X2 interface relation between each RBN and HN.Further, HN may have an X2 interface relation with adjacent BSs.Accordingly, the respective protocol stacks of RBN, HN, and BS have thesame stack structure except for X2-AP for X2 interface that is usedinstead of S1-AP of FIG. 23. HN processes and delivers all X2 messagesbetween RBN and other BSs for all UE-dedicated procedures. X2-AP messageprocessing includes varying S1/X2-AP UE IDs, transport layer addresses,and GTP TEIDs and does not change other portions in the X2 message. Allnon-UE-dedicated X2-AP procedures are terminated in HN and areinternally processed between RBN and HN and between HN and other BSs.Upon receiving X2 non-UE-dedicated message irrelevant to cell from RBNor neighbor BS, HN may trigger corresponding non-UE-dedicated X2-APprocedures for neighbor BS or RBN(s). When receiving cell-related X2non-UE-dedicated message from RBN or neighbor BS, HN may deliverrelevant information to the neighbor BS or RBN(s) based on cellinformation included in the message.

S1 and X2 interface signaling packets are mapped to radio bearersthrough a Ub interface.

FIG. 25 illustrates an example of a wireless control plane protocolstack structure for supporting an operation of an HN and RBN configuringa wireless backhaul according to an embodiment of the presentdisclosure. FIG. 26 illustrates an example of a wireless user planeprotocol stack structure for supporting an operation of an HN and RBNconfiguring a wireless backhaul according to an embodiment of thepresent disclosure.

Referring to FIGS. 25 and 26, RBN is connected with HN through a Ubinterface that uses the same procedure as wireless protocol by which aterminal connects to a base station. An example of wireless controlplane protocol stack of RBN includes non-access stratum (NAS) providingaccess to MME, RRC, PDCP, RLC, MAC, and PHY, and MME includes NAS layeralone, and HN includes the protocols of RBN except for NAS. The userplane protocol stack of RBN and HN include PDCP, RLC, MAC, and PHY.

Further, the following functions are supported for communication of HNand RBN based on the above-described protocol stack structure, accordingto an embodiment of the present disclosure.

RRC layer using a Ub interface performs such function as configuring orreconfiguring a RBN frame for communication between RBN and HN through aRBN reconfiguration procedure. In such case, RBN may request HN toconfigure frame upon RRC connection establishment, and receiving therequest, HN may initiate RRC signaling to configure RBN frame. Throughthe frame configuration function, HN may transfer configurationinformation for switch of operation mode or communication mode ofwireless backhaul to RBN, or RBN may send a request for theconfiguration information to HN and receive the same from HN. Whenreceiving frame configuration information through RRC signaling, RBNapplies the frame configuration information to conduct communicationwith HN in the corresponding operation mode or communication modeaccording to an embodiment of the present disclosure

Further, RRC layer using the Ub interface has a function of includingand delivering newly changed SI in a dedicated message to RBN. By theabove function, HN may transfer, to RBN, SI necessary to switchoperation modes or communication modes of wireless backhaul according toan embodiment of the present disclosure, and RBN may receive and applythe SI to operate in the corresponding mode.

The above-described BUS transition conditions according to an embodimentof the present disclosure may be embodied in the following four cases,and HN and RBN operation may be specified for each case.

The first case is to install new RBN in the wireless backhaul. In thiscase, network OAM transfers a command to transition the HN operationmode into BUS to HN. RBN, when BUS powers on, automatically transitionsthe RBN's operation mode into BUS and operates.

The second case is occurrence of a wireless backhaul link failure. Alink failure of wireless backhaul may occur, e.g., when a building orobstacle newly stands on the wireless backhaul path to cut offcommunication path. HN may set, e.g., a failure to receive, withouterrors and within a predetermined time, a UL response to data or controlinformation transmitted to RBN from RBN, as a reference for determiningthat a failure of link to RBN occurs (hereinafter, “link failuredetermination reference”). According to an embodiment of the presentdisclosure, the link failure determination reference may include when HNfails to receive, without error, UL data at a minimum transmissionspeed. The link failure determination reference may also include when HNfails to consecutively receive BA bits or information a predeterminednumber of times from RBN operating in the LDM of BOCS or fails toreceive them within a predetermined time.

RBN may set a link failure determination reference, e.g., including afailure to detect a sync of the RBN's serving HN, failure to receiveshared control information without error, failure to receive, withouterror, control information of the RBN's serving HN, and failure toreceive without error on DL at a minimum data transmission speed. In thesecond case, when HN identifies that the link failure determinationreference is met, the HN determines to transition the HN's operationmode into BUS and delivers a command for transitioning the operationmode into BUS to the network OAM. Upon meeting the link failuredetermination reference, RBN directly transitions the RBN's operationmode into BUS.

The third case is when link capability deterioration occurs in thewireless backhaul. The link capability deterioration in the wirelessbackhaul may include, e.g., such a circumstance where trees or woods onthe communication path of wireless backhaul flourish to degrade linkcapability or where an object is newly installed to attenuate radiowaves. According to an embodiment of the present disclosure, e.g., whenwireless link capability or quality is continuously left lower than athreshold for a predetermined time may be set as a condition fordetermining the link capability deterioration (hereinafter, “linkcapability deterioration determination condition”). Here, the wirelesslink capability or quality may be determined by, e.g., mean power ofreceived signal per unit radio resource, channel quality indicator (CQI)value, signal-to-noise ratio (SNR), data transmission speed per unitradio resource, and modulation and coding index (MCI) value. As specificexamples, when a maximum value P max (t, t−Ts) of a predeterminedcapability index at a predetermined time interval (e.g., Ts=1 min.)remains worse than a reference capability value (e.g., P(t0)=capabilityvalue achieved by HN-RBN at the latest BUS-to-BOCS switch) by athreshold (e.g., ΔPs=6 dB) or more for a predetermined time (e.g.,Tm=10□), it may be determined that a switch into BUS is needed.

The above example may be represented in Equation 1 as follows:Decide S3, if, for t=t1 to t1−Tm,P max(t,t−Ts)<P(t0)−:ΔPs  Equation (1)

In the third case, when detecting wireless backhaul link capabilitydeterioration based on the above-described link capability deteriorationdetermination condition, HN may report the wireless backhaul linkcapability deterioration to the network OAM. Or, upon detecting thewireless backhaul link capability deterioration, HN may determine totransition the HN's operation mode into BUS and deliver a request fortransitioning operation mode into BUS to the network OAM. Then, HN maytransition into BUS by receiving an operation mode transitioninstruction from the OAM.

In the third case, when receiving a command to transition the operationmode into BUS from the serving HN, RBN transitions into thecorresponding mode.

In the fourth and last case, a transition into BUS may be made at apredetermined period for enhancing performance or in response to aninstruction from the operator. In such case, when receiving a command totransition the operation mode into BUS from the network OAM, HNtransitions into BUS. When receiving an instruction to transition intoBUS from the serving HN, RBN transitions into BUS.

FIGS. 27a and 27b illustrates examples of an operation flow of a firstcase of BUS transition conditions according to an embodiment of thepresent disclosure. In the embodiment shown in FIGS. 27a and 27b , it isassumed that an OAM of network 2710 is requested or instructed toinstall a new RBN 2700 to install the new RBN 2700. Here, information onwhere the new RBN 2700 is installed or information on HN preferred bythe new RBN 2700 or predicted to be linked by the new RBN 2700 may alsobe sent to OAM 2718.

Referring to FIGS. 27a and 27b , when RBN 2700 newly installed powers onin operation 2720 a, the RBN 2700 transitions the operation mode intoBUS in operation 2722.

OAM 2718 having installed the new RBN 2700 in operation 2720 bdetermines HNs having a chance of being linked by the new RBN 2700 andbundles the determined HNs in an HN group operating in the BUS(hereinafter, denoted as “BUS HN group”) in operation 2723. According toan embodiment of the present disclosure, the BUS HN group may beselected using the information on the location of the new RBN 2700 orinformation on HN preferred or predicted to be linked by the new RBN2700 which is included in the request or instruction to install the newRBN 2700. In operations 2724 a and 2724 b, OAM 2718 transfers a commandto transition operation mode into BUS to each HN included in the BUS HNgroup. For ease of description, it is assumed that HN1 27702 and HNn2704 are determined to be in the BUS HN group. In operation 2726, whenreceiving a command to transition operation mode into BUS, HN1 2702 andHNn 2704 each transition into BUS and operate. Here, HN1 2702 and HNn2704 each mark “BUS” on the operation mode in the BCH or beacon frameinformation and broadcast SI necessary for RBNs connected thereto tooperate in the BUS. Further, HN1 2702 and HNn 2704 each transmit SS andBCH slot through all their beams on DL and receive an access orassociation request signal from a corresponding RBN through all theirbeams on UL. They each perform beam training on all the beams to selectthe optimal beam on each of DL and UL.

In operation 2728, the new RBN 2700 operating in the BUS searches orscans HNs while conducting beam training on all reception beams. As aresult, when receiving the SS and BCH or beacon frame information fromHN1 2702 and HNn 2704, the new RBN 2700 detects HN1 2702 and HNn 2704operating in the BUS. In operation 2730, the new RBN 2700 conducts beamtraining on each of the detected HN1 2702 and HNn 2704 to determine theoptimal transmission/reception beam presenting the highest receive powerfor each HN and determine the HN presenting the maximum beam power asthe optimal HN. As an example, it is assumed that HN1 2702 is determinedas the optimal HN.

In operation 2740, the new RBN 2700 then performs a procedure 2740 forinitial access (attach or associate) to the network 2710 through HN12702. First, in operation 2741, the new RBN 2700 sends a RACH preambleor association request signal to HN1 2702 determined as the optimal HN.Here, the new RBN 2700 also transfers a result of measurement made onHN1 2702 in operation 2730 to HN1 2702. When receiving the RACHpreamble, HN1 2702 operates as a serving HN of the new RBN 2700 toprovide a network connection. Accordingly, in operation 2742, HN1 2702delivers time advance (TA) value and scheduling grant to the new RBN2700, and in operation 2743, the HN1 2702 conducts the above-describedRRC connection setup procedure. Through the RRC connection setupprocedure, HN1 2702 and the new RBN 2700 may configure frames fortransitioning the operation mode or communication mode of wirelessbackhaul. In operation 2744, RBN 2700 performs NAS access,authentication, and security procedures with network 2710, and inoperation 2745, MME reports a result of the authentication and securityprocedure performed with the new RBN 2700 to a home subscriber server(HSS) to register the location information on the new RBN 2700.Thereafter, io2746, HN1 2702 and MME generate a session for GTPtunneling described above. According to an embodiment of the presentdisclosure, in operation 2747, the new RBN 2700 then reconfigures aframe for operation in the BUS through RRC connection for HN1 2702, andin operation 2748, HN1 2702 performs S1 context setting with MME.

In operation 2750, the new RBN 2700 sets a configuration for wirelessbackhaul connection. Accordingly, in operation 2751, the new RBN 2700initializes parameters for wireless backhaul connection through OAM 2718and sets up a configuration for the wireless backhaul connection. Inoperation 2752, the new RBN 2700 configures an S1 interface with HN12702, and in operation 2753, HN1 2702 updates the configuration of S1interface of RBN1 2700. In operation 2754, the new RBN 2700 configuresan X2 interface with HN1 2702, and in operation 2755, HN1 2702 updatesthe configuration of X2 interface of RBN1 2700. According to anembodiment of the present disclosure, operations and functions for userplane and control plane through S1 and X2 interface overlap thosedescribed above in connection with FIGS. 20 to 26, and thus, no detaileddescription thereof is given.

Thereafter, in operation 2760 a, HN1 2702, a predetermined time aftercompleting network access and configuration setup of the new RBN 2700,sends a backhaul update status report to OAM 2718. Likewise, when apredetermined time elapses, HNn 2704 in the BUS HN group also delivers abackhaul update status report to OAM 2718 in operation 2760 b.

Upon identifying the reception of the backhaul update status reportsfrom HN1 2702 and HNn 2704 to which operation mode transition commandshave been sent in operations 2724 a and 2724 b, OAM 2718 determineswhether to transition the operation mode of HN1 2702 and HNn 274 intoBOCS in operation 2762. In this case, when the network access procedureof the new RBN 2700 is complete within a predetermined time or failswithin a predetermined time, OAM 2718 may determine to transition theoperation mode of HN1 2702 and HNn 2704 into BOCS. Assuming that theoperation mode of HN1 2702 and HNn 2704 has been determined totransition into BOCS, OAM 2718 delivers commands to transition operationmode into BOCS to HN1 2702 and HNn 2704, respectively, in operations2764 a and 2764 b. Then, in operation 2766, HN1 2702 and HNn 2704 eachtransition into BOCS. HN1 2702 transfers the HN1's transition into BOCSto the new RBN 2700. When receiving a BOCS transition command fromserving HN1 2702, new RBN 2700 in operation 2768 transitions into BOCS.

FIGS. 28a, 29b, and 29c illustrate examples of an operation flow of asecond case of the BUS transition conditions according to an embodimentof the present disclosure.

Referring to FIGS. 28a, 28b, and 28c , in operation 2822 a, a RBN 2800identifies that one of the above-described link failure determinationreferences is met and detects the occurrence of a link failure. RBN 2800may recognize that one of the link failure determination references,e.g., when RBN 2800 fails to receive sync signal, control information,or user data of a serving HN (e.g., HN2 2804) at the RBN 2800's lowestdata speed within a predetermined time as in operation 2821, is met andthus a link failure occurs. In operation 2823, RBN 2800 transitions theRBN 2800's operation mode into BUS.

Meanwhile, in operation 2822 b, a HN2 2804 identifies that one of theabove-described link failure determination references is met and detectsthe occurrence of a link failure. As the link failure determinationreference, HN2 2804 may recognize that a link failure occurs, e.g., whenthere is no UL response from RBN 2800 during a predetermined time as inoperation 2821 or a link failure occurs when the HN2 2804 fails tocontinuously receive BA bits or information a predetermined number oftimes from a RBN operating in the LDM. Then, in operation 2824, HN2 2804delivers a backhaul update request containing a link failure report toan OAM 2818 of network 2810. Here, HN2 2804 may include a measurementresult previously reported by RBN 2800 in the backhaul update request ordetermine candidate HNs having a high chance of being linked by RBN 2800and include information on the determined candidate HNs in the backhaulupdate request. Here, regarding the candidate HNs highly likely to belinked by RBN 2800, it may be determined that the candidate HN having amaximum received power of BM signal in the measurement result has ahigher chance of being linked by RBN 2800. Further, HN2 2804 of RBN 2800may additionally perform disassociation from network 2810 on RBN 2800.

In operation 2825, OAM 2818 determines HNs likely to be accessed by RBN2800 using information on the candidate HNs or measurement result of RBN2800 obtained from the backhaul update request and puts the determinedHNs in one BUS HN group. Hereinafter, operations 2826 a to 2850 aresubstantially the same as operations 2724 a to 2760 b of FIG. 27, andthus, no repetitive description thereof is given.

When receiving, in operation 2850, backhaul update status reports fromHNs (e.g., HN1 2802 and HN2 2804 are assumed) having sent commands totransition operation mode into BUS in operations 2826 a and 2826 b, OAM2818 determines whether to transition the operation mode of HN1 2802 andHN2 2804 into BOCS in operation 2851. It is assumed that the networkaccess procedure by RBN 2800 is complete within a predetermined time orfails within a predetermined time. In such case, OAM 2818 determines totransition the respective operation modes of HN1 2802 and HN2 2804 intoBOCS. In operations 2852 a and 2852 b, OAM 2818 delivers commands totransition operation mode into BOCS to HN1 2802 and HN2 2804,respectively. Then, in operation 2853, HN1 2802 and HN2 2804 eachtransition into BOCS. HN2 2804 transfers the HN2804's transition intoBOCS to RBN 2800. When receiving a BOCS transition command from servingHN2 2804, RBN 2800 in operation 2854 transitions into BOCS.

In another embodiment of the second case among the BUS transitionconditions, the same operations as those described above in connectionwith FIGS. 28a to 28c are performed except for the following:

Specifically, in another exercise of the second case, HN2, which is aserving HN of the RAN having detected a link failure, instead of OAM inthe embodiment of FIG. 28, determines HNs having a chance of beingaccessed by the RBN linked to HN2 and puts the determined HNs in one BUSHN group. Here, among the determined HNs, ones highly likely to beaccessed by the RBN may be selected and used based on the measurementresult or utilizing the measurement result upon detection of the linkfailure from the RBN having detected the link failure.

According to the other embodiment, the serving HN2, instead of OAM,sends a request for transitioning operation mode into BUS or theoperation mode transition command to each HN included in the BUS HNgroup and informs the OAM in the network that HN2 determines totransition operation mode into BUS for the HNs.

According to the other embodiment, the serving HN2 reports thetransition into BUS to the network OAM after a predetermined timeelapses. Further, after a predetermined time passes, each HN included inthe BUS HN group also reports the transition into BUS to the serving HN2and network OAM. When receiving the report for transition into BUS fromthe HNs included in the BUS HN group, the serving HN2 may determinewhether to transition the operation mode of the HNs into BOCS. Forexample, when the network access of RBN having detected the link failureis complete within a predetermined time or fails within a predeterminedtime, the serving HN2 may determine to transition the operation mode ofeach HN included in the BUS HN group into BOCS. Then, the serving HN2sends a request or command for transitioning operation mode into BOCS toeach HN included in the BUS HN group, and the serving HN2 reports to thenetwork OAM that operation mode transition into BOCS of the HNs has beendetermined.

FIGS. 29a, 29b, 29c, and 29d illustrate examples of an operation flow ofa third case of the BUS transition conditions according to an embodimentof the present disclosure.

Referring to FIGS. 29a to 29d , it is assumed that a deterioration oflink capability of a source HN, which is a serving HN, is detected todetermine a transition of operation mode into BUS in operation 2918.Then, in operation 2920, source HN 2902 sends a backhaul update requestto an OAM 2916. Here, the backhaul update request may include ameasurement result received by the source HN from a RBN 2900 connectedthereto or information on candidate HNs highly likely to be accessed bythe RBN determined by the source HN.

When receiving the backhaul update request, OAM 2916 in operation 2921determines HNs likely to be accessed by RBN 2900 based on themeasurement result of RBN 2900 or information on the candidate HNshighly likely to be accessed by RBN 2900 obtained from the backhaulupdate request and puts the determined HNs in one BUS HN group. Anexample is assumed in which the BUS HN group includes a source HN 2902and a target HN 2904. Then, in operations 2922 a and 2922 b, OAM 2916delivers commands to transition operation mode into BUS to source HN2902 and target HN 2904, respectively. In operation 2923, source HN 2902and target HN 2904 transit the HN 2902's operation mode and the targetHN 2904's operation mode into BUS and operate, respectively. Here,source HN 2902 and target HN 2904 mark “BUS” on their operation modes inBCH or beacon frame information and broadcast SI necessary for RBNs tooperate in the BUS. Further, source HN 2902 and target HN 2904 each sendSS and BCH slot through all their beams on DL and receive RACH signal orassociation request signal for access by RBN through all their beams onUL to discover the optimal beam among all their beams on each of DL andUL.

When receiving, in operation 2924, operation mode indication informationindicating that the operation mode of source HN 2902 is the BUS from theserving HN of RBN 2900, i.e., source HN 2902, RBN 2900 transitions theRBN 2900's operation mode into BUS in operation 2924. In operation 2925,source HN 2902 instructs RBN 2900 to do BM. Here, in operations 2926 aand 2926 b, communication of packet data is possible between source HN2902 and RBN 2900, and packet data communication is possible betweensource HN 2902 and GW 2914 of network 2910.

In operation 2926 c, source HN 2902 assigns a UL resource of RBN 2900.Then, in operation 2927, RBN 2900 performs BM measurement based on theUL resource to detect HNs operating in the BUS as well as source HN 2902and performs BM measurement on the detected HNs and sends a result ofthe measurement to source HN 2902. When receiving the BM measurementresult from RBN 2900, source HN 2902, in operation 2928, identifieswhether there is HN capable of providing higher-quality communication toRBN 2900 and determines a handover of RBN 2900. For example, when the HNhaving the maximum beam receive power known from the BM measurementresult of RBN is not source HN 2902 but another HN, the other HN (e.g.,it is assumed to be target HN 2904) is selected as a target HN forhandover.

Then, in the embodiment shown in FIGS. 29a to 29d , a handoverpreparation procedure A is performed through operations 2929 to 2933.First, operation 2929, source HN 2902 sends a handover request to targetHN 2904. In operation 2930, the target HN identifies whether access byRBN is acceptable, and when acceptable, the target HN sends a handoverrequest acknowledgement to source HN 2902 to accept access by RBN 2900in operation 2931. Then, in operation 2932, source HN 2902 assign DLresource of RBN 2900 and in operation 2933, sends a RRC message based onthe DL resource to instruct a handover to target HN 2904 and sendshandover-related information.

When the handover preparation procedure A is complete, a handoverrunning procedure B is performed through operations 2934 to 2940. Inoperation 2934, the RBN releases connection with source HN 2902, and inoperation 2935, source HN 2902 determines to deliver packet datasupposed to be transmitted to RBN 2900 and stored in the buffer totarget HN 2904. In operation 2936, source HN 2902 sends a packetsequence number (SN) status transmission message to target HN 2904, andin operation 2936, forwards the packet data supposed to be transmittedto RBN 2900 and stored in the RBN 2900's buffer to target HN 2904.Accordingly, in operation 2938, target HN 2904 stores the data packetsforwarded from source HN 2902 in the buffer.

In operation 2939, RBN 2900 sends a RACH signal or association requestto access target HN 2904. Then, in operation 2940, target HN 2904delivers UL resource allocation information of RBN 2900 and TA value forUL. Target HN 2904 also sends a response to the association request.When RBN 2900 successfully access target HN 2904, the target HN 2904sends a RRC message to target RBN 2904 to report that the handover issuccessfully done and also sends relevant information in operation 2941.

When the handover running procedure B is complete, target HN 2904, likein operation 2942 a, may send packet data to RBN 2900. A handovercomplete procedure C is performed through operations 2943 to 2950.

In operation 2943, target HN 2904 sends a path switch request to a MME2912 to report that the serving HN linked to RBN 2900 has been changedinto target HN 2904. Then, in operation 2944, MME 2912 delivers a modifybearer request to an S-GW 2910. Then, in operation 2945, S-GW 2910switches the path of DL data for RBN 2900 into target HN 2904.Accordingly, when DL packet data occurs, the DL packet data istransferred to target HN 2904, rather than source HN 2902, as inoperation 2946.

Thereafter, in operation 2947, S-GW 2914 sends a modify bearer responsemessage to MME 2912. Then, in operation 2948, MME 2912 sends a pathswitch request acknowledgement message to target HN 2904 in response tothe path switch request. In operation 2949, target HN 2904 sends a RBNcontext release message to source HN 2902 to inform that the handover ofRBN 2900 to target HN 2904 has been successfully done and to triggerresource release of source HN 2902. When receiving the RBN contextrelease message, source HN 2902 releases wireless and control-relatedresources related to RBN 2900 in operation 2950. In operation 2951,source HN 2902 delivers a backhaul update status report includinginformation on the handover result of RBN 2900 to OAM 2916 after apredetermined time elapses. Further, when a predetermined time elapses,the HNs included in the BUS HN group also deliver backhaul update statusreports to source HN 2902 and OAM 2916.

Upon identifying the reception of the backhaul update status reportsfrom source HN 2902 and target HN 2904 to which operation modetransition commands have been sent in operations 2922 a and 2922 b, OAM2916 determines whether to transition the operation mode of source HN2902 and target HN 2904 into BOCS in operation 2952. In this case, whena link capability enhancement of RBN 2900 is complete within apredetermined time or fails within a predetermined time, OAM 2916 maydetermine to transition the operation mode of source HN 2902 and targetHN 2904 into BOCS. Assuming that the operation mode of source HN 2902and target HN 2904 has been determined to transition into BOCS, OAM 2916delivers commands to transition operation mode into BOCS to source HN2902 and target HN 2904, respectively, in operations 2753 a and 2753 b.Then, in operation 2954, source HN 2902 and target HN 2904 eachtransition into BOCS. Target HN 2904 transfers the target HN 2904'stransition into BOCS to RBN 2900. When receiving the same, RBN 2900transitions into BOCS in operation 2955.

In another embodiment of the third case among the BUS transitionconditions, the same operations as those described above in connectionwith FIGS. 29a to 29d are performed except for the following:

Specifically, in another embodiment of the third case, the source HN,instead of OAM, determines HNs having a chance of being accessed by theRBN linked to source HN and puts the determined HNs in one BUS HN group.The BUS HN group may be selected using the measurement result of the RBNor information on the candidate HNs highly likely to be accessed by theRBN. The source HN delivers a request or command for transitionoperation mode into BUS to the HNs included in the BUS HN group andreports to the OAM that an operation mode transition into BUS of the HNsin the BUS HN group has been determined. According to anotherembodiment, the source HN, instead of the OAM, determines whether totransition the operation mode of the HNs in the BUS HN group into BOCS.Here, when a link capability enhancement of the RBN is complete within apredetermined time or fails within a predetermined time, the HNs may bedetermined to transition into BOCS. The source HN, instead of the OAM,delivers a request or command for transitioning operation mode into BOCSto the HNs in the BUS HN group, and the source HN further reports thedetermination of transition of the operation mode of the HNs into thenBOCS to the OAM.

FIG. 30 illustrates an example of an operation flow of a fourth case ofthe BUS transition conditions according to an embodiment of the presentdisclosure.

Referring to FIG. 30, it is assumed that in operation 3020, a serving HN3002 of a RBN 3000 detects a deterioration of link capability anddetermines to request to update backhaul. Accordingly, in operation3022, serving HN 3002 delivers a backhaul update request to an OAM 3012of a network 3010. Here, the backhaul update request may include ameasurement result received from RBN 3000 or information on candidateHNs highly likely to be accessed by RBN 3000 determined by source HN3002 based on the BM result. In operation 3012, OAM 3012 having receivedthe backhaul update request determines HNs likely to be accessed by RBN3000 using information on the candidate HNs or measurement resultobtained from the backhaul update request and puts the determined HNs inone BUS HN group. Here, assuming that serving HN 3002 and an adjacent HN3004 are in the BUS HN group, OAM 3012, in operations 3026 a and 3026 b,delivers a command to transition operation mode into BUS to each of theHNs, i.e., serving HN 3002 and adjacent HN 3004, of the BUS HN group.

When receiving the operation mode transition command, serving HN 3002and adjacent HN 3004 each transition into BUS and operate in operation3027. Here, serving HN 3002 and adjacent HN 3004 each puts a markindicating that the serving HN 3002's operation mode and the adjacent HN3004's operation mode, respectively, into the BUS on the BCH andbroadcasts SI necessary for RBNs linked thereto to operate in the BUS.Further, serving HN 3002 and adjacent HN 3004 transmit SS and BCH forall the beams on DL, receive RACH through all the RACH's beams on UL,and select the optimal beam by conducting BM on DL and UL.

In operation 3028, when receiving BCH broadcast from serving HN 3002 andidentifying that the operation mode of serving HN 3002 is the BUS, RBN3000 transitions into BUS and operates.

In operation 3029, serving HN 3002 instructs RBN 3000 to conduct BM, andin operation 3030, serving HN 3002 delivers UL resource allocationinformation for RBN 3000 to RBN 3000. In operation 3031, RBN 3000detects adjacent HNs, e.g., adjacent HN 3004, operating in the BUS, aswell as serving HN 3002 using a UL resource corresponding to the ULresource allocation information, conducts BM measurement on the detectedadjacent HNs, and reports a result to serving HN 3002.

In operation 3032, upon identifying that there is a communication pathin a different direction which provides higher-quality communication toRBN 3000 based on the BM result, serving HN 3002 determines to changebeams for RBN 3000, and in operation 3040, serving HN 3002 conducts abeam changing procedure on RBN 3000. Specifically, in operation 3041,serving HN 3002 instructs RBN 3000 to send a RACH signal in a new beam.Pursuant to the instruction, in operation 3042, RBN 3000 sends a RACHsignal in the new beam. When receiving the RACH signal, serving HN 3002in operation 3043 gives a UL TA value to RBN 3000 and instructs RBN 3000to change and use the new beam. A wireless backhaul adopting the IEEE802.11ad wireless LAN standard changes optimal beams without RACH signaltransmission/reception in operation 3042 and TA value transfer processin operation 3043 among the operations constituting the beam changingprocedure 3040.

Thereafter, in operation 3050 a, serving HN 3002 delivers a backhaulupdate status report containing information on the beam change of RBN300 to OAM 3012. Further, in operation 3050 b, the HNs, i.e., adjacentHN 3004, in the BUS HN group also deliver backhaul update status reportsto serving HN 3002 and OAM 3012 when a predetermined time elapses.

Upon identifying the reception of the backhaul update status reportsfrom source HN 3002 and adjacent HN 3004 to which operation modetransition commands have been sent in operations 3026 a and 3026 b, OAM3012 determines whether to transition the operation mode of source HN3002 and neighbor HN 3004 into BOCS in operation 3051. In this case,when a link capability enhancement of RBN 3000 is complete within apredetermined time or fails within a predetermined time, OAM 3012 maydetermine to transition the operation mode of source HN 3002 andadjacent HN 3004 into BOCS. Assuming that the operation mode of sourceHN 3002 and adjacent HN 3004 has been determined to transition intoBOCS, OAM 3000 delivers commands to transition operation mode into BOCSto source HN 3002 and adjacent HN 3004, respectively, in operations 3052a and 3052 b. Then, in operation 3053, source HN 3002 and adjacent HN3004 each transition into BOCS. Adjacent HN 3004 transfers the HN 3004'stransition into BOCS to RBN 3000. When receiving the same, RBN 3000transitions into BOCS in operation 3054.

In another embodiment of the fourth case among the BUS transitionconditions, the same operations as those described above in connectionwith FIG. 30 are performed except for the following:

Specifically, in another embodiment of the fourth case, the serving HN,instead of OAM, determines HNs having a chance of being accessed by theRBN linked to source HN and puts the determined HNs in one BUS HN group.The BUS HN group may be selected using the measurement result of the RBNor information on the candidate HNs highly likely to be accessed by theRBN. The serving HN delivers a request or command for transitionoperation mode into BUS to the HNs included in the BUS HN group andadditionally reports to the OAM that an operation mode transition intoBUS of the HNs in the BUS HN group has been determined. According toanother embodiment, the serving HN determines whether to transition theoperation mode of the HNs in the BUS HN group into BOCS. Here, when alink capability enhancement of the RBN is complete within apredetermined time or fails within a predetermined time, the HNs may bedetermined to transition into BOCS. The serving HN, instead of the OAM,delivers a request or command for transitioning operation mode into BOCSto the HNs in the BUS HN group, and the serving HN further reports thedetermination of transition of the operation mode of the HNs into thenBOCS to the OAM.

Further, according to another embodiment, the procedures shown in FIGS.29 and 30 may be performed at predetermined periods or by the operator'sinstruction to enhance capability.

FIG. 31 illustrates an operation flow of a RBN according to anembodiment of the present disclosure. In connection with the embodimentshown in FIG. 31, RBN is assumed to be a RBN that attempts initialaccess to a network in a wireless backhaul or reaccesses the networkafter a link failure occurs.

When powering on or detecting a link failure in operation 3102, RBNtransitions into BUS in operation 3104. Through operations 3106 to 3110,RBN stands by for detecting at least one HN that has transitioned intoBUS. Specifically, RBN in operation 3106 searches for HNs using all theRBN's beams, and in operation 3108, receives the BCH of a searched HN toobtain shared control information of the HN. In operation 3110, RBNidentifies whether the operation mode of the detected HN is the BUS.Unless the identification result shows that the operation mode of thedetected HN is the BUS, RBN returns to operation 3106 to search for HNs.

When the operation mode of the detected HN is identified as the BUS, RBNin operation 3112 measures the receive power of alltransmission/reception beam combinations on the detected HN. Inoperation 3114, RBN discovers the optimal transmission/reception beamcombination giving the maximum receive power for each detected HN andfurther discovers the optimal HN (HNopt) having the maximum receivepower. In operation 3116, RBN sends a RACH preamble to HNopt, accessesand generates a wireless backhaul link, initializes parameters for thelink and sets up a configuration, and reports the BM result to HNopt. Inoperation 3118, RBN identifies whether the operation mode of HNopt,which is the serving HN, is the BOCS. When the operation mode of HNoptis identified to be the BOCS, RBN in operation 3120 transitions intoBOCS and operates. When the operation mode of HNopt is identified to bethe BUS, RBN in operation 3122 maintains the current operation mode.

FIG. 32 is a view illustrating an operation flow of a RBN according toanother embodiment of the present disclosure. RBN in the embodimentshown in FIG. 32 is assumed to be a RBN detecting a link capabilitydeterioration of wireless backhaul to change serving HNs or beams.

When identifying that the operation mode of serving HN is the BUSthrough shared control information of BCH received from serving HN inoperation 3202, RBN transitions into BUS and operates in operation 3204.In operation 3206, RBN searches for HNs with all the RBN's beams, and inoperation 3208, RBN performs BM for measuring the receive power of alltransmission/reception beam combinations on the detected HNs. Inoperation 3210, RBN reports the measurement result to serving HN.

In operation 3212, RBN identifies whether an instruction to hand over tothe target HN is received from the serving HN. When the handoverinstruction is identified to be received, RBN in operation 3216 handsover to the target HN and goes to operation 3220. Unless the handoverinstruction is received, RBN proceeds with operation 3214. In operation3214, RAN identifies whether to receive an instruction to change into anew beam from the serving HN. When the instruction to change isidentified to be received, RBN in operation 3218 sends a RACH preambleto serving HN using the new beam as instructed by serving HN, receives aTA for the new beam from serving HN, and communicates with serving HNusing the new beam.

In operation 3220, RBN identifies whether the operation mode of servingHN is the BOCS. When the operation mode of serving HN is identified tobe the BOCS, RBN in operation 3222 transitions into BOCS and operates.When the operation mode of serving HN is identified to be the BUS, RBNin operation 3224 maintains the current operation mode.

Meanwhile, according to an embodiment of the present disclosure, hewireless backhaul may optimize capability through an operation modetransition. As shown in FIG. 3, a transition between communication modesis possible while RBN is operating in the BOCS, thereby leading tofurther enhanced capability. Among the communication modes, ABM maysupport a mitigation of capability deterioration that occurs due to aninfluence from external environment. Transition condition and operationsbetween communication modes according to an embodiment of the presentdisclosure may be specified as follows:

Referring to FIG. 3, a transition (a) from FBM 342 to ABM 344 may bemade under the environment that the antenna of HN or RBN is swayed by anexternal influence, e.g., a strong wind gust, resulting in the magnitudeof received signal fluctuating.

According to an embodiment of the present disclosure, as a reference oftransition (a), FBM-to-ABM transition (a) may be determined to be madewhen, in order to detect such a phenomenon that wireless channelcharacteristics of serving HN and RBN are varied over time, and amonglink capabilities, the receive power of signal per unit radio resourcefor RBN or AGC of receiver is varied over time, the difference betweenthe maxium value P max(t, t−Ta) and minimum value Pmin(t, t−Ta) of linkcapability index within a predetermined time interval (e.g., Ta=onemin.) is larger than a threshold (e.g., :ΔPa=6 dB), and the time duringwhich the difference is larger than the threshold lasts a predeterminedtime (e.g., Tm=10 min.) or longer.

Transition (a) may be represented in Equation 2 below:Decide M1, if, for t=t1˜t1−Tm,P max(t,t−Ta)−P min(t,t−Ta)>:ΔPa.  Equation (2)

Upon meeting the transition (a) reference, serving HN determines totransition the communication mode of RBN from FBM to ABM, assigns DL BMslot or UL BM slot, or DL and UL BM slot, and instructs RBN to performDL BM or UL BM, or DL and UL BM. Then, HN and RBN conduct beammeasurement according to an embodiment of the present disclosure. The DLoptimal beam is determined by RBN, and the UL optimal beam is determinedby HN. Or, according to an embodiment of the present disclosure, BM isperformed only on DL, and UL may use a UL beam in the same direction asthat of the DL optimal beam. Alternatively, BM may be performed only onUL, and DL may use a DL beam in the same direction as that of the ULoptimal beam. According to an embodiment of the present disclosure, HNand RBN may perform adjustment so that the BM range encompasses theoptimal beam while monitoring the variation in the optimal beam in athree-dimensional (3D) beam direction and adaptively varying the beamrange to be measured. Further, according to an embodiment of the presentdisclosure, when each of a plurality of RBNs linked to one serving HNmeasures BM, the number of DL or UL beams may be different per RBN.

Next, referring to FIG. 3, as a reference for a transition (b) from ABM344 to FBM 342, a transition into FBM may be made upon meeting atransition (b) reference where the optimal beam is not varied for apredetermined time in ABM. For example, when the optimal beams ofserving HN and RBN operating in ABM for 10 or 30 minutes are not varied,transition (b) into FBM may be determined to be made. Then, according toan embodiment of the present disclosure, serving HN determines acommunication mode transition of RBN and delivers a command totransition communication mode into FBM to RBN without assigning DL andUL BM slot to RBN.

Referring to FIG. 3, in a case where a transition (f) is made from FBMto LDM, e.g., upon meeting such a transition (f) reference in which BSinstalled in RBN operates in LDM, RBN may send a request fortransitioning communication mode into LDM to serving HN.

When receiving the request for transitioning communication mode into LDMfrom RBN, serving HN determines DL paging period, UL scheduling request(SR) period, UL BA bit or information transmission period which are tobe used when RBN operates in LDM and informs RBN. Then, RBN receives DLcontrol information at each DL paging period to determine whether pagingis present, has a chance of transmitting an SR bit at the uplinkscheduling request period, and sends a BA bit at each UL BA bittransmission period. RBN sends BA bits for all the RBN's BA bittransmission times while operating in LDM.

Referring to FIG. 3, in a transition (e) from LDM 346 to FBM 342 or atransition (d) to ABM 344, e.g., when paging is received on DL by a UElocated in the coverage of RBN-BS may be set as a mode transitioncondition in LDM. As another example, when RBN sends a UL SR bit orinformation to transmit UL information or data on UL may be determinedas a mode transition condition in LDM.

When the above-described mode transition condition in LDM is met, acommunication mode prior to transition into LDM is identified, and atransition is made corresponding to the prior communication mode.Specifically, when the prior communication mode is FBM, a transitioninto FBM is made, and when the prior communication mode is ABM, atransition into ABM is made. Or, according to an embodiment of thepresent disclosure, FBM may be set as default, so that a communicationmode transition in LDM always is made to FBM or ABM selectively. Whenmeeting the mode transition condition in LDM as set forth above, RBNtransitions into the prior communication mode or default communicationmode and may use the optimal beam used to be used in the priorcommunication mode.

Referring to FIG. 3, in a transition (c) from ABM 344 to LDM, liketransition (f), when BS of RBN is operated in LDM may be set as atransition (c) condition. When the transition (c) condition is met, RBNsends a request for switching communication mode into LDM to serving HN.When receiving the communication mode switching request, serving HNdetermines DL paging period, UL SR period, UL BA bit or informationtransmission period which are to be used when RBN operates in LDM andinforms RBN. RBN operating in LDM receives DL control information ateach DL paging period to determine whether there is paging, has a chanceof sending an SR bit at UL SR period, and sends a BA bit at each UL BAbit period. Here, RBN sends BA bits for all the RBN's BA bittransmission times while operating in LDM.

Meanwhile, according to an embodiment of the present disclosure, when HNand RBN transition their operation mode from BUS to BOCS, FBM or ABM maybe selected as a default communication mode of RBN.

FIG. 33 is a view illustrating an example of an operation mode of an HNoperated as a BOCS and a communication mode transition operationaccording to an embodiment of the present disclosure.

Referring to FIG. 33, in operation 3300, HN identifies whether toreceive a command to switch operation mode into BUS from an OAM ofnetwork or adjacent HN. When the command of switching operation modeinto BUS is identified to be received, HN in operation 3338 transitionsoperation mode into BUS. In such case, according to an embodiment of thepresent disclosure, HN may perform the operations described above inconnection with FIGS. 27 to 30.

Unless the command of switching operation mode into BUS is identified tobe received, HN in operation 3302 identifies whether the communicationmode of RBN linked to HN is LDM. When the communication mode isidentified to be LDM, HN in operation 3304 identifies whether BA bit orinformation is received from RBN at least once without error during apredetermined BA period. When no BS bit or information is identified tobe received during the BS period, HN in operation 3306 detects awireless backhaul link failure between HN and RBN and transitions intoBUS. In such case, HN having transitioned into BUS may operate accordingto the embodiment shown in FIG. 28. In this case, HN may correspond toHN2 of FIG. 28.

When BA is identified in operation 3304 to be received at least once ormore, HN in operation 3308 determines that the wireless backhaul linkwith RBN is maintained and identifies whether SR bit or information isreceived from RBN to send UL data or control information, whether thereis data to be sent on DL from HN to RBN, or whether paging is receivedfrom a MS linked to BS of RBN. As a result of the identification, uponmeeting one of when SR bit or information is received, when there isdata to be sent on DL, and when paging is received from MS, HN inoperation 3310 switches the communication mode of RBN from FBM to ABMand conduct wireless backhaul communication. Here, the communicationmode switch of RBN is operated corresponding to the operations relatedto transition (e) and transition (d) described above in connection withFIG. 3. As a result of the identification, when none of when SR bit orinformation is received, when there is data to be sent on DL, and whenpaging is received from MS are met, HN and RBN in operation 3312maintain their current communication modes BOCS and LDM.

When the communication mode of RBN is identified in operation 3302 to benot LDM, HN in operation 3312 identifies whether a UL response to DLcontrol information or data is received from RBN within a predeterminedtime without error. As a result of the identification, when a ULresponse to DL control information or data is not received within thepredetermined time or received information has an error, HN determinesthat a wireless backhaul link failure occurs between HN and RBN and HNin operation 3336 transitions the HN's operation mode into BUS. In thiscase, HN performs an operation corresponding to HN2 of FIG. 28.

When a UL response to DL control information or data is identified inoperation 3312 to be received within the predetermined time, HN inoperation 3314 identifies whether to receive a request for transitioningcommunication mode into LDM from RBN. When the request for transitioningcommunication mode into LDM is identified to be received, HN inoperation 3316 delivers the request for transitioning communication modeinto LDM to RBN. In this case, a transition operation is performedcorresponding to transition (c) and transition (f) of FIG. 3. Unless therequest for transitioning communication mode into LDM is identified tobe received, HN in operation 3318 identifies whether the communicationmode of RBN is FBM.

When the communication mode of RBN is FBM, HN in operation 3320identifies whether link capability for RBN is poor during a timedetermined as in Equation 1 described above. When the link capability isidentified to be poor, HN in operation 3322 determines that a wirelessbackhaul link capability deterioration for RBN occurs and transitionsthe HN's operation mode into BUS. In this case, HN may performoperations corresponding to those shown in FIG. 29 or 30. Here, HN mayoperate as the source HN of FIG. 29 or serving HN of FIG. 30.

When the link capability of RBN is identified in operation 3320 to benot poor during the time, HN in operation 3324 identifies whether avariation in the wireless backhaul link capability for RBN is largerthan a threshold, e.g., during a time determined as in Equation 2. Whenthe variation in the link capability is identified to be larger than thethreshold, HN in operation 3326 transitions the communication mode ofRBN into ABM. Here, HN operates corresponding to the transition (a)operation described above in connection with FIG. 3. When the variationin the link capability is identified to be equal or smaller than thethreshold, HN and RBN in operation 3328 maintain the current operationmodes and communication modes, i.e., BOCS and FBM.

When the communication mode of RBN is identified in operation 3318 to benot FBM, HN in operation 3330 identifies whether the optimal beam forRBN is changed during a predetermined time. When the optimal beam ischanged, HN and RBN in operation 3332 maintain the current operationmodes and communication modes, i.e., BOCS and ABM. When the optimal beamis identified to be not changed, HN in operation 3334 transitions thecommunication mode of RBN into FBM. In this case, HN operatescorresponding to the transition (b) operation described above inconnection with FIG. 3.

FIG. 34 is a view illustrating an example of a configuration of abackhaul node and RAN according to an embodiment of the presentdisclosure. The configuration of the backhaul node and RAN of FIG. 34 ismerely an example for illustrative purposes, and according to anembodiment of the present disclosure, the configuration may be brokendown into more detailed functional units, modules, components, devices,or the backhaul node and RAN components may be integrated into a singleunit or varied to fit the business provider's intention.

Referring to FIG. 34, backhaul node 3410 corresponds to an HN or RBNaccording to an embodiment of the present disclosure, and RANcorresponds to a MBS or SBS.

Backhaul node 3410 includes, e.g., a transceiver unit 3418, a radiofrequency (RF) unit 3416, a processor 3412, and a memory 3414, and RAN3430 includes a processor 3432, a memory 3434, a RF unit 3436, and atransceiver unit 3438. Backhaul node 3410 is connected with a networkvia element 3440 and is connected with RAN 3430 via element 3420.According to an embodiment of the present disclosure, processor 3412performs wireless backhaul communication functions includingtransmission and reception of wireless backhaul data, wireless backhaulcontrol information, and various wireless backhaul signals and a controlfunction for wireless backhaul operation, and memory 3414 stores variouswireless backhaul data, control information, and signals. Processor 3412controls RF unit 3416 and connects with RF unit 3416 to communicatesignals. RF unit 3416 is connected with transceiver unit 3418 tocommunicate RF signals. Here, processor 3412 controls transceiver unit3418 and RF unit 3416 to select and control transmission/reception beamsgenerated by transceiver unit 3418 and RF unit 3416. Processor 3412 maybe implemented in hardware, a control processing unit (CPU) andsoftware, or in both hardware and software. As described above inconnection with the structure shown in FIG. 18, backhaul node 3410 andRAN 3430 may be implemented in various structures, and reference number3420 may be a communication cable connecting the devices, a backplaneconnecting boards, or a bus connecting chips on the same board. Thenetwork connection via element 3440 may be implemented wiredly orwirelessly through another backhaul node. When backhaul node 3410 is anHN, and element 3440 is connected to a RBN which is another backhaulnode, a multi-hop or wireless mesh network may be established. Whenbackhaul node 3410 is a RBN, element 3440 may be omitted.

In sum, as described above, according to an embodiment of the presentdisclosure, a wireless backhaul may be operated in only one of twooperation modes, i.e., BUS and BOCS, leading to optimized wirelessbackhaul capability and minimized costs necessary for installation andoperation of wireless backhaul device. Further, according to anembodiment of the present disclosure, a wireless backhaul providesoperation mode transition references and methods. According to anembodiment of the present disclosure, a wireless backhaul provides suchfunctionality as to transition operation mode into BUS when a new RBN isinstalled to automatically discover the optimal HN and optimaltransmission/reception beam for the new RBN, link to the optimal HN,provide network connection, and establish the optimal wireless backhaullink. As a result, costs for installation of a new RBN may be minimized.

Further, according to an embodiment of the present disclosure, awireless backhaul provides such functionality as to transition operationmode into BUS upon detecting a link failure between HN and RBN orcapability deterioration due to a variation in communication environmentof a wireless backhaul already established to discover a new optimal HNand optimal transmission/reception beam providing higher-qualitycommunication to a RBN for which a capability deterioration has beendetected, link to the new optimal HN, provide network connection, andrestore the wireless backhaul link. Resultantly, costs (OPEX) incurredduring the course of wireless backhaul operation may be minimized.

Further, according to an embodiment of the present disclosure, awireless backhaul provides such functionality as to transition operationmode into BUS when a variation in communication environment of awireless backhaul already established is varied to cause a deteriorationin communication capability of HN and RBN, and the network determines anoperation mode switch due to the link capability deterioration todiscover a transmission/reception beam corresponding to a new optimalcommunication path providing higher-quality communication to a RBNsuffering from a communication capability deterioration, allow the sameto change beams, and optimize wireless backhaul link capability. Also inthis case, costs incurred during the course of wireless backhauloperation may be minimized.

According to an embodiment of the present disclosure, a wirelessbackhaul, upon determining that the wireless backhaul is operated in BUSto achieve a target value, transitions into BOCS to conduct optimizedwireless communication using only the optimal transmission/receptionbeam. In order to maximize efficiency while minimizing waste of radioresources in BOCS, according to an embodiment of the present disclosure,HN sends SS and BCH on DL using some limited beams among all the HN'sbeams that are able to be transmitted or received by the HN's antennafor only RBNs linked to HN, thus minimizing interference and waste ofradio resources on DL and optimizing capability. Further, BM forselecting the optimal beam among all DL and UL beams is not supported,but rather, limited beam tracking is supported only on some candidatebeams adjacent to the optimal beam, thereby leading to minimized wasteof radio resources for beam measurement, along with increased beammeasurement efficiency and performance. No RACH preamble or associationrequest signal for access to HN of RBN is transmitted or received on UL,thus allowing for minimized interference and waste of UL radio resourcesand optimized capability.

According to an embodiment of the present disclosure, a wirelessbackhaul may be implemented using a cellular mobile communicationstandard adopting beamforming technology or using the IEEE 802.11adbeamforming wireless LAN standard. However, according to an embodimentof the present disclosure, in BOCS, a wireless backhaul supports onlysome functions, but not all of the functions of mobile communication orwireless LAN communication as per the standard.

According to an embodiment of the present disclosure, when operated inBOCS, RBN operates in only one communication mode of FBM, ABM, and LDM,leading to a further enhancement in efficiency and performance ofwireless backhaul. According to an embodiment of the present disclosure,in a wireless backhaul, HN and RBN communicate in FBM of BOCS withoutchanging the optimal transmission/reception beam discovered in BUS anddoes not communicate beam measurement signals for beam measurement andbeam change, thus increasing radio resource use efficiency. FBM presentsthe optimal communication performance in most of fixed wireless backhaulcommunication environments where communication environment is notsubject to change. According to an embodiment of the present disclosure,a wireless backhaul provides such functionality as to minimize adeterioration of performance due to external environments since HN orRBN additionally conducts level-limited BM in ABM of BOCS. Further, inABM, limitation is imposed on the beam range measured, thus allowing forreduced waste of radio resources for beam measurement, increasedcommunication efficiency, and reduced beam measurement period and thewireless backhaul's resultant enhancement in beam adaptation capability.

Further, according to an embodiment of the present disclosure, awireless backhaul may provide such functionality as to allow RBN totransition into LDM of BOCS to minimize power consumption andinterference with other wireless backhaul. Use of LDM may maximize thepower use efficiency of wireless backhaul while allowing other wirelessbackhaul enhanced communication performance. However, when the wirelessbackhaul needs to conduct normal communication, the wireless backhaulmay transition into another communication mode of BOCS at HN'sinstruction or RBN's request and conduct wireless backhaulcommunication. Here, upon requesting to transition into thecommunication mode, RBN sends SR bit or information rather than UL RACHsignal. Thus, waste of UL radio resources may be reduced, andcommunication efficiency may be increased. According to an embodiment ofthe present disclosure, in a wireless backhaul, RBN operating in LDMsends BA bit or information to serving HN at each predetermined period,thereby periodically reminding serving HN that the wireless backhaullink is not disconnected but alive. As a result, for RBN operating inLDM, HN may simply determine whether the wireless backhaul link faces aproblem, and upon detecting a link failure, the HN enables a quickrestoration of wireless backhaul.

As is apparent from the foregoing description, according to anembodiment of the present disclosure, the wireless backhaul isdistinctively operated in a state of being operated using all the beamsor in a state where communication is carried out using only the optimalbeam, wherein the state where communication is carried out using onlythe optimal beam is operated distinctively in a mode where a fixed beamis used, a mode where limited beam measurement is additionally conductedon beams adjacent to the optimal beam, and a power save mode in whichsignal transmission is made only at predetermined periods. Thus, thecapability of wireless backhaul may be optimized, and costs forinstallation and operation of wireless backhaul apparatus may beminimized.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for providing a connection with a radioaccess network via a wireless backhaul, the method comprising:determining one of a first state in which a first node connected withthe radio access network is operated using a plurality of beams or asecond state in which the first node is operated using a beam of thefirst node as an operation mode of the first node; providing, by thefirst node, the connection with a base station using the operation mode;based on identifying that the operation mode of the first node is thesecond state, sending, by the first node, a sync signal and a sharedcontrol information to at least one second node connected to the firstnode using the beam of the first node; and sending, by the first node, acontrol signal and data for the wireless backhaul to the at least onesecond node connected to the first node, using the beam of the firstnode without supporting the first node to access a new second node whileoperating in the second state.
 2. The method of claim 1, furthercomprising determining a communication mode of the at least one secondnode connected with the base station based on identifying that theoperation mode of the first node is the second state.
 3. The method ofclaim 2, wherein determining the communication mode includes selectingat least one of a first mode in which the at least one second nodeperforms communication using a fixed beam combination to the first node,a second mode in which beam measurement is performed using beamsadjacent to a beam constituting the fixed beam combination, or a thirdmode in which a signal is sent only at a predetermined period.
 4. Themethod of claim 3, further comprising transitioning the at least onesecond node into the second mode based on identifying that the at leastone second node connected to the first node operating in the first modemaintains a difference between a maximum value and minimum value forreception capability that is larger than a threshold for a predeterminedtime.
 5. The method of claim 3, further comprising transitioning the atleast one second node into the first mode based on identifying that theat least one second node connected to the first node operating in thesecond mode maintains a beam of the at least one second node for apredetermined time.
 6. The method of claim 3, further comprisingtransitioning the at least one second node into the first mode or thesecond mode based on identifying that the first node receives ascheduling request from the at least one second node connected to thefirst node and operating in the third mode.
 7. The method of claim 1,further comprising determining to transit the operation mode of thefirst node from the second state to the first state upon meeting one ofa first case where a new node connected with the radio access network isadded to the wireless backhaul while the first node is operated in thesecond state, or a second case where a node having a failure orcapability deterioration of a link with the first node is detected. 8.The method of claim 1, wherein the base station is at least one of amacro base station or small cell base station providing a mobilecommunication service.
 9. An apparatus for providing a connection with aradio access network via a wireless backhaul, the apparatus comprising:a transceiver configured to communicate with a first node connected withthe radio access network; and a controller configured to: determine atleast one of a first state in which the first node is operated using aplurality of beams or a second state in which the first node is operatedusing a beam of the first node as an operation mode of the first node;determine one or more beams to send a sync signal and shared controlinformation based on the operation mode; control transceiver to providethe connection with a base station using the determined operation mode;and based on identifying that the operation mode of the first node isthe second state: control the transceiver to send a sync signal and ashared control information to at least one second node connected to thefirst node using the beam of the first node, and control the transceiverto send a control signal and data for the wireless backhaul to the atleast one second node connected to the first node, using the beam of thefirst node without supporting the first node to access a new second nodewhile operating in the second state.
 10. The apparatus of claim 9,wherein the controller is further configured to determine acommunication mode of the at least one second node connected with thebase station based on identifying that the operation mode of the firstnode the second state.
 11. The apparatus of claim 10, wherein thecontroller is further configured to select at least one of a first modein which the at least one second node performs communication using afixed beam combination to the first node, a second mode in which beammeasurement is performed using beams adjacent to a beam constituting thefixed beam combination, or a third mode in which a signal is sent onlyat a predetermined period.
 12. The apparatus of claim 11, wherein thecontroller is further configured to determine a transition of the atleast one second node into the second mode based on identifying that theat least one second node connected to the first node operating in thefirst mode maintains a difference between a maximum value and minimumvalue for reception capability that is larger than a threshold for apredetermined time.
 13. The apparatus of claim 11, wherein thecontroller is further configured to determine a transition of the atleast one second node into the first mode based on identifying that theat least one second node connected to the first node operating in thesecond mode maintains a beam of the at least one second node for apredetermined time.
 14. The apparatus of claim 11, wherein thecontroller is further configured to determine a transition of the atleast one second node into at least one of the first mode or the atleast one second mode based on identifying that the first node receivesa scheduling request from the second node connected to the first nodeand operating in the third mode.
 15. The apparatus of claim 9, whereinthe controller is further configured to determine to transit theoperation mode of the first node from the second state to the firststate upon meeting at least one of a first chase where a new nodeconnected with the radio access network is added to the wirelessbackhaul while the first node is operated in the second state, or asecond case where a node having a failure or a capability deteriorationof a link with the first node is detected.
 16. The apparatus of claim 9,wherein the base station is at least one of a macro base station orsmall cell base station providing a mobile communication service.